Combustion Engines and Hybrid Propulsion Systems Contenido 1. 2. 3. 4. 5. Ideal cycles................................................................................................................................................... 1 1.1. Otto cycle............................................................................................................................................. 2 1.2. Diesel cycle .......................................................................................................................................... 3 1.3. Sabathe Cycle ...................................................................................................................................... 4 1.4. Indicated mean effective pressure ...................................................................................................... 4 Real cycles ................................................................................................................................................... 5 Questions/problems Cycles ......................................................................................................................... 6 Combustion in spark ignition (SI) engines ................................................................................................. 10 4.1. Classification of combustion types .................................................................................................... 10 4.2. Spark ignition concept and 2-zone model ......................................................................................... 10 4.3. First law of thermodynamics in the view of combustion engine ...................................................... 11 4.4. Describe the process of heat release ................................................................................................ 11 4.5. Describe the basic types of spark ignition combustion chambers .................................................... 12 4.6. Describe stratified combustion systems which utilize direct injection ............................................. 12 Engine performance and efficiency ........................................................................................................... 13 5.1. Definitions of engine performance parameters and fuel consumption............................................ 13 1. Draw and describe energy flow through the engine ............................................................................. 13 2. Provide definitions of brake mean effective pressure, brake specific fuel consumption, indicated mean effective pressure, indicates specific fuel consumption. .................................................................... 14 3. Explain changes in thermal efficiency at variable engine load or speed, provide approximate values.14 4. Explain changes in mechanical efficiency at variable engine load or speed, provide approximate values. ............................................................................................................................................................ 14 6. 5. Calculate engine torque and power for given IMEP, mechanical efficiency, swept volume and speed. 15 6. Calculate specific fuel consumption for given fuel mass flow and power. ........................................... 15 7. Calculate thermal efficiency having fuel consumption, lower heating value, swept volume and IMEP. 15 8. Draw and explain engine efficiency on specific fuel consumption map. .............................................. 15 1. Fuels........................................................................................................................................................... 17 Classify fuels according to different criteria. ......................................................................................... 17 2. Shortly characterise main engine fuels (mineral and renewable). ....................................................... 17 3. Critically evaluate biofuels in aspects of production feasibility, engine compatibility and overall carbon footprint. ........................................................................................................................................... 18 4. Describe chemical composition of gasoline, diesel fuel, natural gas, LGP. ........................................... 18 5. Provide names and definitions of the main fuel properties.................................................................. 19 6. What is lower/higher heating value and how this parameter can be calculated? Roughly calculate heating values for fuels with given chemical formula (e.g. propane C3H8) or composition (given C, H, 0). 20 7. Calculate mass-based theoretical air requirements of fuel for given chemical formula or composition. (In case of propane)....................................................................................................................................... 20 8. Calculate volume-based theoretical air requirement of fuel for a given chemical formula (e.g., methane, propane, ethanol, methanol, DME (CH3-O- CH3))........................................................................ 20 7. Engine Exhaust Composition ..................................................................................................................... 21 1. Calculate exhaust composition for stoichiometric mixture of fuel with known molecule or composition. .................................................................................................................................................. 21 2. List toxic exhaust components emitted by IC engines. ......................................................................... 21 3. Provide approximate exhaust composition of spark ignition or diesel engine. .................................... 21 4. Describe changes in diesel engine exhaust composition at variable load ............................................ 21 5. Describe sources of unburnt hydrocarbons emissions. ........................................................................ 22 6. Describe sources of CO emission........................................................................................................... 22 7. Describe conditions for NOx formation................................................................................................. 22 8. Describe process of particulate matter formation ................................................................................ 22 9. What physical properties of exhaust compounds are utilised for measurement of their concentrations. .............................................................................................................................................. 23 8. 10. Which fuel and engine properties affect CO2 emission. ................................................................... 23 11. Calculate CO2 emission for given composition and fuel consumption. ............................................ 23 1. Hybrid electric vehicles.............................................................................................................................. 24 Provide definition of hybrid power train. .............................................................................................. 24 2. List few types of power sources used in hybrid powertrains. ............................................................... 24 3. Explain the idea of hybridization – indicate how energy efficiency is increased. ................................. 24 4. List and explain benefits from hybridization. ........................................................................................ 24 5. List and define different stages of hybridization. .................................................................................. 25 6. Describe in detail and draw design of different hybrid powertrains (parallel, series, series-parallel, slit axle, split power). Provide pros and cons...................................................................................................... 25 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 1. Ideal cycles The thermodynamic cycles that take place in the engine replace real cycles, so that the study of it is simplified. The basic and fundamental parameters that support the thermodynamic behavior of the engine are imposed. The following assumptions are made: • The fluid that evolves is an ideal gas. • The ideal gas equation is used. • The specific heat is considered constant with temperature. Aire: ρ = 1.293ππππ/ππ3 ππππ = 0.24 ππππππππ/ππππππ = 1 ππππ/ππππππ (1004.67 ππππ/ππππππ) πππ£π£ = 0.1715 ππππππππ/ππππππ = 0.72 ππππ/ππππππ (717.63 π½π½/ππππππ) ππ Γ = ππ = 1.3 • • • • • πππ£π£ The internal energy of the fluid will only depend on the temperature. The fluid does not change throughout the cycle. Heat is transferred and supplied instantaneously. The valves open and close instantaneously. Compression and expansion without an increase in entropy. IDEAL GAS PHYSICAL EQUATIONS Boyle-Mariotte Law: ππππ = ππππππ Gay-Lussac Law: ππ = ππππππ ππ ππππ = ππππππ ππ Clapyron Law (General eq.): Si Δππ = 0 → V cp ln V2 1 Polytropic approaching: 1 (isobaric process) ππ = ππ0 (1 + απ‘π‘) ; α = 273 Charles Gay-Lussac Law: Adiabatic approaching: (isothermal process) (isochoric process) 1 mol in n.c.; R=cte; ππ ππ Δππ = ππ2 − ππ1 = ππππππ ππππ ππ2 + πππππ£π£ ππππ ππ2 P + cv In P2 1 =0→ V ln V2 cv 1 γ ππ2 ππ2 → ππππ = ππππππ ππ cp = = γ ππ1 ππ1 1 P −ln P2 1 1 ππ γ ππ γ ππ → ππππ οΏ½ππ2 οΏ½ = ππππ ππ1 → οΏ½ππ2 οΏ½ = ππ2 → γ 1 → ππππ = ππππππ ππ πΎπΎ ππ1 ππ−1 ππ2 ππππ ππ = πΎπΎ ππππ οΏ½ = = ππππππ → ππ ππ−1 ⋅ ππ = ππππππ → οΏ½ οΏ½ = ππππ = ππππππ ππππ ππππππ ππ2 ππ1 ππππ ππ πΎπΎ ππ1 ππππ ππ = πΎπΎ 1−ππ ππ οΏ½ οΏ½ οΏ½ ππ ππ = = ππππππ → ππ ⋅ ππ = ππππππ → ππ ππ (ππππ) = (ππππππ) ππ ππ (ππππππ)ππ ππ2 ππ = ππππππ → ππ2 ππ1 1 − ππ ππ1 ππ−1 ππ = ππππππ → =οΏ½ οΏ½ =οΏ½ οΏ½ οΏ½ ππ = ππππππ → ππ1 ππ2 ππ ππ2 ππ = ππππππ → 1 ππ PV = nRT 2 1−ππ ππ ππ = 0 ππ = 1 ππ = πΎπΎ ππ = ∞ = 1 ππ2 ππ1 1 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 1.1. Otto cycle The Otto cycle is the ideal cycle associated with gasoline or spark-ignition engines. This cycle is not exactly the same as experienced in reality, as mentioned earlier, however, it allows for explaining the process under simple assumptions. Phases: 0-1. Intake at constant pressure (atmospheric). 1-2. Compression at constant entropy and increase in temperature. 2-3. Combustion (instantaneous) at constant volume, pressure increases. 3-4. Expansion at constant entropy. Temperature and pressure decrease. 4-1. Exhaust of combustion gases and pressure drop. The heat input inside the engine is Q1, it is carried out at constant volume, so the work in that phase will be zero, so it can be reached: Δππ = ππ − ππ → ππ1 = πππ£π£ (ππ3 − ππ2 ) The same applies to heat loss: ππ2 = πππ£π£ (ππ4 − ππ1 ) The thermal efficiency is the product of the work done and the energy given up. η= ππ1 − ππ2 πππ£π£ (ππ3 − ππ2 ) − πππ£π£ (ππ4 − ππ1 ) = πππ£π£ (ππ3 − ππ2 ) ππ1 The compression and expansion processes are adiabatic, so, using the equations for adiabatic processes, this equation is simplified. ππ1 γ−1 ππ2 ππ =οΏ½ οΏ½ ; ππ2 = ππ3 β« ππ1 οΏ½1 − ππ4 οΏ½ βͺ ππ2 ππ3 ππ1 − ππ4 ππ1 1 1 ππ1 ππ2 1 = →η=1− =1− =1− =1− =1− γ−1 ππ ππ ππ3 − ππ2 ππ2 2 ππ4 ππ3 ππ1 γ−1 β¬ ππ1 ππ4 ππ2 οΏ½ππ3 − 1οΏ½ οΏ½ οΏ½ =οΏ½ οΏ½ ; ππ1 = ππ4 βͺ ππ 2 1 ππ2 ππ4 ππ3 β The compression ratio is the quotient of the air volume at bottom dead centre and top dead centre. ππ = ππ1 /ππ2 η=1− 1 ππ γ−1 οΏ½ππ1 οΏ½ 2 =1− 1 ππ γ−1 The thermal efficiency of the Otto cycle will be dependent on the compression ratio and the ratio of specific heats. It does not depend on the heat input. 2 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 1.2. Diesel cycle The diesel cycle is the ideal cycle associated with compression ignition engines. The difference with the Otto cycle lies in the heat input phase, where in the diesel cycle the heat is produced at constant pressure, whereas in the Otto cycle it is produced at constant volume. In addition, higher compression ratios are generally used in diesel engines. In Otto engines, the compression ratios are much lower, as combustion control would not be possible. 0-1.Air intake at constant pressuer (atmospheric). 1-2. Isentropic compression. 2-3. Combustion at constant pressure (instantaneous ignition). 3-4. Isoentropic expansion. 4-1. Exhaust of combustion gases. The heat supply process is carried out at constant pressure, so that the piston moves and work is done. ππ1 = Δππ + (ππ3 ππ3 − ππ2 ππ2 ) ; β = ππ + ππππ → ππ1 = β3 − β2 = ππππ (ππ3 − ππ2 ) The expansion takes place at constant volume, so the heat lost will be: ππ2 = πππ£π£ (ππ4 − ππ1 ) The thermal efficiency will be calculated as the quotient of the work done and the heat given up. As in the Otto cycle, ideal gas thermodynamic tools will be used to obtain a more manageable expression. η= ππππ (ππ3 − ππ2 ) − πππ£π£ (ππ4 − ππ1 ) 1 ππ4 − ππ1 =1− (ππ ) ππππ 3 − ππ2 γ ππ3 − ππ2 ππ4 1 ππ1 οΏ½ππ1 − 1οΏ½ =1− γ ππ οΏ½ππ3 − 1οΏ½ 2 ππ 2 ππ3 γ−1 ππ4 ππ3 ππ4 = οΏ½ οΏ½ ππ1 ππ2 ππ2 ππ1 ππ ππ The injection ratio is known as the degree of heat input at constant pressure. ππππ = ππ3 = ππ3 1 ππππ γ−1 γ ππππ −1 ππ4 γ 1 ππ1 οΏ½ππ1 − 1οΏ½ 1 1 ππ − 1 η=1− = 1 − γ−1 ππ γ ππ οΏ½ππ3 − 1οΏ½ γ ππ ππππ − 1 2 ππ 2 2 2 > 1 This product is always greater than 1, so it is something that makes the performance relative to the Otto lower. However, this is not entirely true. The reality is that diesel engines are not the same as petrol engines. Diesel engines are built so that when they reach the point of combustion, the fuel reaches a certain temperature to promote the burning of the fuel without the need for an external element (spark). Diesel engines have a much higher compression ratio than petrol engines. At equal compression ratio: ηππππππππ > ηππππππππππππ 3 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 1.3. Sabathe Cycle Cycles in reality differ from the theoretical ideal cycles. Diesel engines, for example, operate in real life, where the combustion process takes place partly at constant volume and partly at constant pressure. In the Sabathé cycle, this phenomenon was specifically studied in order to establish a more accurate approximation of the thermodynamic behaviour of the engine. ππ1 = ππ1′ + ππ1′′ ππ1′ = πππ£π£ (ππ3 − ππ2 ) ππ1′′ = ππππ (ππ4 − ππ3 ) ππ2 = πππ£π£ (ππ5 − ππ1 ) η=1− πππ£π£ (ππ5 − ππ1 ) ππ5 − ππ1 =1− (ππ ) (ππ ) (ππ πππ£π£ 3 − ππ2 + ππππ 4 − ππ3 3 − ππ2 ) + γ(ππ4 − ππ3 ) Knowing that process 2-3 is at constant volume, 3-4 at constant pressure and 1-2 and 4-5 are adiabatic:: ππ3 ππ3 = ππ2 ππ2 ππ4 γ−1 οΏ½ ππ5 ππ2 ππ3 ππ5 οΏ½ ππ4 ππ3 ππ4 γ−1 = = οΏ½ οΏ½ ππ1 ππ4 ππ3 ππ2 γ−1 ππ3 ππ2 ππ2 οΏ½ππ οΏ½ 1 ππ4 ππ4 = ππ3 ππ3 ππ5 ππ5 ππ3 ππ4 γ γ−1 − 1 − 1 ππ1 ππ1 ππ2 ππ1 ππ1 ππ2 οΏ½ππ2 οΏ½ − 1 η=1− =1− =1−οΏ½ οΏ½ ππ ππ ππ ππ2 οΏ½ππ3 − 1οΏ½ + γ οΏ½ππ4 − ππ3 οΏ½ ππ2 οΏ½ππ3 − 1οΏ½ + γ T3 οΏ½ππ4 − 1οΏ½ ππ1 οΏ½ππ3 οΏ½ + γ ππ3 οΏ½ππ4 − 1οΏ½ ππ2 ππ2 ππ2 T2 ππ3 2 2 3 Knowing the compression ratio (ππ = ππ ππ1 ), ππ2 the injection ratio (ππππ = ππ4 ππ3 = ππ4 ). ππ2 In addition, the constant volume compression ratioλ = ππ3 is introduced. The thermal efficiency can be expressed as: 2 γ λππππ − 1 1 γ−1 Diésel → λ = 1 η=1−οΏ½ οΏ½ οΏ½ (λ − 1) + γλ(ππππ − 1) Otto → ππππ = 1 ππ 1.4. Indicated mean effective pressure The pressure of the fluid inside the engine varies at each instant, so the calculation of the work done by the engine would require a complex calculation. This is why the average pressure of the cycle is used to approximate these parameters. The area of the rectangle represents the work done per cycle. The height of this rectangle represents the average pressure of that cycle. The base of the triangle is the engine displacement. 4 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 2. Real cycles Real cycles consider energy losses or different conditions that reduce engine efficiency. These phenomena include: 1. 2. 3. 4. 5. 6. Leakages Progressive combustion Imcomplete combustion Heat losses Time losses Exhaust losses • Compression In this process, the mixture of air, water and waste gases (from the previous combustion) is compressed. There is a small temperature gradient, so it can be assumed to be an adiabatic and practically reversible process. • Combustion During combustion, in positive ignition engines (MEP), the flame speed that causes the mixture to ignite is not of the same order of magnitude as the linear speed of the piston. This phenomenon is known as timing losses. Given this phenomenon, ignition in the chamber is not instantaneous and temperature imbalances occur, a phenomenon known as creeping combustion. The average temperature of thermal energy input is lower, decreasing the efficiency. The engine has to be cooled so that its components do not suffer high thermal stresses, so that thermal energy is lost through heat loss. Combustion is not complete, due to some of the phenomena described above. • Expansion Exhaust losses are experienced, due to heat losses resulting from the expansion process and the temperature difference between fluid and environment. This graph shows the PV diagram of a positive-ignition combustion engine and all the losses associated with the phenomena described above. In the following, the actual behaviour of the engine will be studied in more detail for each particular case. It is usually assumed that the evolving fluid is air, otherwise the idealisation of the process is very complicated. 5 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 3. Questions/problems Cycles 1. Draw Otto, Diesel or Sabathe Cycle with description of the subsequent processes. The diesel cycle is the ideal cycle associated with compression ignition engines. The difference with the Otto cycle lies in the heat input phase, where in the diesel cycle the heat is produced at constant pressure, whereas in the Otto cycle it is produced at constant volume. In addition, higher compression ratios are generally used in diesel engines. In Otto engines, the compression ratios are much lower, as combustion control would not be possible. 0-1.Air intake at constant pressuer (atmospheric). 1-2. Isentropic compression. 2-3. Combustion at constant pressure (instantaneous ignition). 3-4. Isoentropic expansion. 4-1. Exhaust of combustion gases. 2. Compare theoretical and real cycles for diesel and spark ignition engines. Real cycles consider energy losses or different conditions that reduce engine efficiency. These phenomena include: 1. 2. 3. 4. 5. 6. Leakages Progressive combustion Imcomplete combustion Heat losses Time losses Exhaust losses • Compression In this process, the mixture of air, water and waste gases (from the previous combustion) is compressed. There is a small temperature gradient, so it can be assumed to be an adiabatic and practically reversible process. • Combustion During combustion, in positive ignition engines (MEP), the flame speed that causes the mixture to ignite is not of the same order of magnitude as the linear speed of the piston. This phenomenon is known as timing losses. Given this phenomenon, ignition in the chamber is not instantaneous and temperature imbalances occur, a phenomenon known as creeping combustion. The average temperature of thermal energy input is lower, decreasing the efficiency. The engine has to be cooled so that its components do not suffer high thermal stresses, so that thermal energy is lost through heat loss. Combustion is not complete, due to some of the phenomena described above. • Expansion Exhaust losses are experienced, due to heat losses resulting from the expansion process and the temperature difference between fluid and environment. 6 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes This graph shows the PV diagram of a positive-ignition combustion engine and all the losses associated with the phenomena described above. In the following, the actual behaviour of the engine will be studied in more detail for each particular case. It is usually assumed that the evolving fluid is air, otherwise the idealisation of the process is very complicated. 3. Compare efficiency of different cycles. The thermal efficiency in the Otto cycle is defined by the following equation: η=1− 1 γ−1 ππ οΏ½ππ1 οΏ½ 2 The thermal efficiency in the Diesel cycle is defined by: 1 ππππ γ−1 γ ππππ −1 =1− 1 ππ γ−1 ππ4 γ 1 ππ1 οΏ½ππ1 − 1οΏ½ 1 1 ππππ − 1 η=1− = 1 − γ−1 γ ππ οΏ½ππ3 − 1οΏ½ γ ππ ππππ − 1 2 ππ 2 > 1 This product is always greater than 1, so it is something that makes the performance relative to the Otto lower. However, this is not entirely true. The reality is that diesel engines are not the same as petrol engines. Diesel engines are built so that when they reach the point of combustion, the fuel reaches a certain temperature to promote the burning of the fuel without the need for an external element (spark). Diesel engines have a much higher compression ratio than petrol engines. At equal compression ratio: ηππππππππ > ηππππππππππππ 4. What is indicated mean effective pressure, draw graphical interpretation of IMEP. The pressure of the fluid inside the engine varies at each instant, so the calculation of the work done by the engine would require a complex calculation. This is why the average pressure of the cycle is used to approximate these parameters. The area of the rectangle represents the work done per cycle. The height of this rectangle represents the average pressure of that cycle. The base of the triangle is the engine displacement. 7 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 5. Design theoretical Sabathe cycle for the following data: π·π·ππ = ππ. ππ π΄π΄π΄π΄π΄π΄ π»π»ππ = ππππππππ π½π½ππ = ππππππ ππππππ πͺπͺπͺπͺ = ππππ πΈπΈππ = ππππππ π±π± πΈπΈππ = ππππππππ V CR = V1 → CR = 2 1-2: V2 +Vs V2 πΎπΎ V = 1 + Vs → V2 = 35.71 cm3 2 πΎπΎ ππ1 = ππ2 + πππ π = 535.71 ππππ3 ππ ⋅ ππ πΎπΎ = ππππππ → ππ1 ππ1 = ππ2 ππ2 → ππ2 = ππ1 πΆπΆπ π πΎπΎ = 3.38 ππππππ πΎπΎ−1 ππ ⋅ ππ πΎπΎ−1 = ππππππ → ππ1 ππ1 2-3: πΎπΎ−1 = ππ2 ππ2 → ππ2 = ππ1 πΆπΆπ π πΎπΎ−1 = 651.22 πΎπΎ ππ2 = ππ3 = 35.71 ππππ3 ππππ = ππππππ → ππ = ππ1 ππ1 = 6.46 ⋅ 10−4 ππππ π π π π ππππ = ππππππ (ππ3 − ππ2 ) → ππ3 = ππ2 + ππππ = 1730.71 πΎπΎ ππππππ ππ2 ππ3 ππ3 ππ = ππππππ → = → ππ3 = ππ2 = 8.98 ππππππ ππ2 ππ4 ππ2 ππ 3-4: ππ3 = ππ4 = 8.98 ππππππ ππππ = ππππππ (ππ4 − ππ3 ) → ππ4 = ππ3 + ππππ = ππππππ → ππ4 = 4-5: ππππππ4 = 51.62 ππππ3 ππ4 ππ1 = ππ5 = 535.71 ππππ3 πΎπΎ ππππ = ππππππ → πΎπΎ ππ4 ππ4 ππππ = 2500 πΎπΎ ππππππ = πΎπΎ ππ5 ππ5 πΎπΎ−1 ππ ⋅ ππ πΎπΎ−1 = ππππππ → ππ4 ππ4 ππ4 πΎπΎ → ππ5 = ππ4 οΏ½ οΏ½ = 0.43 ππππππ ππ5 πΎπΎ−1 = ππ5 ππ5 → ππ5 = ππ4 πΆπΆπ π πΎπΎ−1 = 1239.1 πΎπΎ 8 Máquinas Marinas y Sistemas de Propulsión 1 1. V1=535.71 cm3 P1=0.1 MPa T1=289 K 5. V5=535.71 cm3 P5=0.43 MPa T5=1239.1 K 2. Apuntes V2=35.71 cm3 P2=3.38 MPa T2=651.22 K 3. V3=35.71 cm3 P3=8.98 MPa T3=1730.17 K 6. Calculated indicated thermal efficiency for the following data: ππππππππ ππππ ππππππππ = ππππ ππππ π΄π΄π΄π΄ π³π³π³π³π³π³ = ππππ ππππ π°π°π°π°π°π°π°π° = ππ. ππ π΄π΄π΄π΄π΄π΄ π½π½ππ = ππππππ ππππππ πΌπΌπΌπΌπΌπΌπΌπΌ = ππ → ππ = πΌπΌπΌπΌπΌπΌπΌπΌ ⋅ ππππ = 0.8 ⋅ 500 = 400 π½π½ ππππ ππβ = πΏπΏπΏπΏπΏπΏ ⋅ ππππ = 40 ⋅ 106 ⋅ 40 ⋅ 10−6 = 1600 π½π½ ππ = 400 ππ = = 0.25 ππ 1600 9 4. V4=51.62 cm3 P4=8.98 MPa T4=2500 K Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 4. Combustion in spark ignition (SI) engines 4.1. Classification of combustion types Regarding the space where fuel and oxidizer are mixed, we can spot different classifications: Homogeneous charge combustion: The fuel and air are well mixed before combustion, resulting in a homogeneous mixture. The mixture is then compressed to a temperature and pressure and pressure that cause ignition to occur simultaneously across the entire mixture. This results in a clean and efficient combustion process with reduced emissions. Diffusion combustion: The fuel and oxidizer are brought together but not well mixed, leading to combustion occurring gradually as the mixture diffuses through the surrounding air. The reaction front moves slowly and the flame temperature is relatively low. According to the mechanism of combustion: Deflagration: Subsonic reaction front that propagates through a reactive mixture. In a deflagration, the reaction front moves at a velocity slower than the speed of sound in the reactive mixture. As a result, the pressure increase in front of the reaction front is gradual, and the reaction is less likely to result in a explosion or shock wave. Kinetic combustion: The combustion is dominated by chemical kinetics rather than fluid mechanics. In other words, the rate of reaction is determined by the chemical properties of the reactants and the energy required for the reaction to occur, rather than the mixing and transport of the reactants. This type of combustion is often used in high-speed and high-temperature combustion processed. The chemical kinetics of the reaction determine the ignition delay, reaction rate, and product distribution. 4.2. Spark ignition concept and 2-zone model The combustion process is initiated by a spark from a spark plug. The spark ignites a mixture of fuel and air, which then burns and generates power. Spark ignition engines are commonly used in gasoline-powered vehicles and are known for their simplicity, reliability, and ease of maintenance. The spark timing and spark duration can be adjusted to optimize the combustion process, resulting in improved efficiency and reduced emissions. The basic components of a spark ignition engine include the spark plug, ignition coil, distributor, and control module. The 2 zone.model of combustion in spark ignition engine refers to a simplified representation of the combustion process in an internal combustion engine. According to the 2-zone model, the combustion chamber is divided into two zones: a premixed zone, where the fuel and air are well mixed, and a diffusion zone, where the mixture is burned by a flame front that propagates through the unburned mixture. The 2zone model assumes that the premixed zone burns instantaneously and that the flame front then spreads through the diffusion zone, consuming the remaining mixture. The flame propagation front can be understood as a laminar flame front velocity or turbulent. The common speed in the laminar front is around 0.1 ms-1, in the turbulent front is 30-60 ms-1- The burning in the laminar propagation is made in normal direction, while the turbulent is not clear at all and it could knock into different front shape. 10 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 4.3. First law of thermodynamics in the view of combustion engine The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transformed from one form to another. In the context of a combustion engine, this law applies to the energy transfer and transformations that occur during the combustion process. The first law of thermodynamics can be expressed mathematically as the energy balance equation, which states that the change in internal energy of a closed system is equal to the heat added to the system minus the work done by the system. This equation can be written as: Δππ = ππ − ππ In a combustion engine, the closed system of the engine and its surroundings. The internal energy of the system changes as a result of heat transfer from the combustion of fuel and work done by the engine. The heat added to the system is the energy released by the combustion of fuel, and the work done by the system is the mechanical power generated by the engine. This equation can be rewrite: ππ2 dππ = ππ ⋅ ππππ ⋅ ππππ + οΏ½ ππ ⋅ ππππ + ππππβπ‘π‘ ππ1 Also, rearranging from the ideal gases equation the temperature field we can obtain: ππ = ππ⋅ππ ππ⋅π π ππ2 ππ2 ππππ ππππ = ππππ οΏ½ − ππ1 ππ1 οΏ½+ ππππ ππ(ππ2 − ππ1 ) + ππππβπ‘π‘ This equation can be manipulated to calculate the pressure changing field in the camber, given the heat release ratio (dU). 4.4. Describe the process of heat release Heat release in a spark ignition engine refers to the process by which heat energy Is generated and transferred from the combustion of fuel to the engine’s cylinders, where it is used to do work. The process of heat release in a spark ignition engine typically involves the following steps: 1. Fuel-air mixture preparation: Fuel and air are mixed in the carburetor or fuel injectors to create a homogeneous mixture of fuel and air, which is the drawn into the engine’s cylinders. 2. Compression stroke: The piston moves upwards, compressing the fuel-air mixture in the cylinder. The compression of the mixture increases the temperature and pressure, creating ideal conditions for combustion. 3. Spark ignition: A spark from the spark plug ignites the fuel-air mixture in the cylinder, initiating the combustion process. The heat generated by the combustion reaction raises the temperature of the cylinder and its contents. 4. Heat release: The heat generated by the combustion is transferred from the cylinder to the engine’s coolant, which circulates through the engine and carries the heat away. The heat energy is then used to generate mechanical power by expanding and pushing the piston. 5. Expansion stroke: The expansion of the hot gas pushes the piston downwards, generating mechanical power and driving the crankshaft. The expansion also cools the gas, reducing its temperature and pressure. 6. Exhaust stroke: The exhaust valve opens, allowing the hot, burned gases to escape from the cylinder. The cylinder is then ready for the next cycle to begin. The process of heat release in a spark ignition engine is repeated many times per second, generating mechanical power and driving the engine’s crankshaft. 11 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 4.5. Describe the basic types of spark ignition combustion chambers There are several basic types of spark ignition combustion chambers: 1. Flat top piston: A flat top piston with a small dish shape provides a relatively large surface area for the fuel-air mixture mixture to ignite, resulting in a stable flame front and efficient combustion. 2. Hemispherical head: A semispherical head with a rounded surface provides a compact combustion chamber with good mixture good mixture swirl, resulting in improved combustion efficiency and recuded emissions. 3. Tumble-type: A tumple-type combustion chamber uses specific design features to promote fuel-air mixing and improve combustion efficiency, including complex shapes and contours that promote turbulence and mixing of the fuel-air mixture. 4. Pent-roof: A pent-roof combustion chamber uses specific design features to promote fuel-air mixing and improve combustion efficiency, including complex shapes and contours that promote turbulence and mixing of the fuel-air mixture. 5. Bathtub: A bathtub combustion chamber features a raised floor and sidewalls that surround the spark plug, providing a well-defined combustion space that helps to promote efficient combustion and reduce emissions. 4.6. Describe stratified combustion systems which utilize direct injection Stratified combustion systems refer to engine designs that use direct injection technology to create a more controlled and efficient combustion process. The main advantage of this system is that it can provide a higher level of control over the air-fuel mixture, resulting in improved fuel economy, lower emissions, and better performance. In a stratified combustion system, the fuel is delivered directly into the combustion chamber in a precisely controlled manner, creating a localized concentration of fuel in the region around the spark plug. This concentration of fuel provides the energy required to start and sustain the combustion process, while the remaining air in the combustion chamber helps to control the flame speed and reduce emissions. The basic components of a direct injection system include a high- pressure fuel pump, injectors, and a control system that manages the timing and quantity of fuel delivered to the engine. The control system uses sensors to monitor engine parameters such as speed, load and temperature, and adjusts the fuel delivery accordingly to ensure optimal performance and efficiency. In practice, the direct injection system is used in combination with other engine management technologies, such as variable valve timing, to provide a more flexible and efficient combustion process. This approach can help to improve engine efficiency and reduce emissions, specially in high-performance and high-load applications. Overall, stratified combustion systems represent a major advance in the technology of spark ignition engine, offering improved performance and efficiency while reducing emissions and enhancing the driving experience. 12 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 5. Engine performance and efficiency 5.1. Definitions of engine performance parameters and fuel consumption The torque is a measure of the engine’s rotational force, typically expressed in Newtons meters. It is the twisting force that allows the engine to turn the wheels and move the vehicle. Effective, or brake torque refer to the torque at crankshaft end. Effective torque is measured on an engine dynamometer test stand. The effective torque is proportional to the effective work: ππ ππππ = ππ⋅ππππ ;ππ is the number of strokes To express engine performance, it is convenient to use parameters that are related to engine displaced volume. The most frequently used measure for engine load is brake mean effective pressure. π΅π΅π΅π΅π΅π΅π΅π΅ = The engine effective power is set as: ππππ πππ π ππππ = ππππ ⋅ ππ = ππππ ⋅ ππ 9550 The indicated parameters are those which are measure before the mechanical gear of the engine. Those measures are done right after the thermodynamical cycle. The effective measures are those which we can truly experiment in matter of mechanical energy. We can discuss mechanical and thermal efficiency as: ππππ πππ‘π‘β = ππ ππβ = ∫ ππππππ ππππ ⋅πΏπΏπΏπΏπΏπΏ ππ ππππ = ππππ = ππ ππππ ⋅ππ⋅ππ ∫ ππππππ The indicated specific fuel consumption (ISFC) is a measure of the fuel efficiency of an internal combustion engine, typically expressed in g/kWh. It represents the amount of fuel consumed per unit of power output and is often used to compare the fuel efficiency of different engine designs. The lower the ISFC, the more efficient the engine is at converting fuel energy into useful work. πΌπΌπΌπΌπΌπΌπΌπΌ = ππππ ππππ 1. Draw and describe energy flow through the engine The energy flow through an internal combustion engine can be described as follows: 1. Fuel and air mixture enters the engine’s combustion chamber and is compressed by the pistons. 2. The compressed mixture is then ignited by a spark from the spark plug, causing an explosion. 3. The energy from the explosion pushes the pistons down, converting the energy of the explosion into mechanical energy. 4. The mechanical energy from the pistons is transferred to the crankshaft, which converts it into rotational energy. 5. The rotational energy from the crankshaft is transmitted to the transmission, which converts It into forward motion of the vehicle. 6. Some energy is also lost as heat due to friction and other inefficiencies in the engine and its components. πΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆ → πΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆπΆ → ππππππβππππππππππππ ππππππππππππ → π π π π π π π π π π π π π π π π π π π π ππππππππππππ → ππππππππππππ ππππ π£π£π£π£βππππππππ → πΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈ ππππππππππππ 13 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 2. Provide definitions of brake mean effective pressure, brake specific fuel consumption, indicated mean effective pressure, indicates specific fuel consumption. Brake mean effective pressure (BMEP): It is a measure of the average pressure acting on an engine’s pistons during a complete engine cycle. It is used to determine an engine’s efficiency and power output. BMEP is calculated by dividing the total work done by the engine over a complete cycle by the engine’s swept volume. A higher BMEP value indicates a more efficient engine with higher power output, while a lower value means the engine is less efficient and has lower power output. Brake specific fuel consumption: 3. Explain changes in thermal efficiency at variable engine load or speed, provide approximate values. Thermal efficiency is the ratio of useful work output from an engine to the energy input as heat. It can be affected by several factors including engine load, speed, and design features such as exhaust gas recirculation and pumping losses. At low engine load and low speeds, pumping losses increase as the engine has to work harder to draw in air and fuel, reducing thermal efficiency. Exhaust gas recirculation, which recirculates a portion of the engine’s exhaust gases back into the combustion chamber, can also decrease thermal efficiency at low loads as it dilutes the oxygen concentration in the combustion chamber, making combustion less complete. At high engine loads and high speeds, thermal efficiency improves as the engine operates closer to its maximum design potential, and pumping losses are reduced. Exhaust gas recirculation can also increase thermal efficiency at high loads by reducing peak cylinder pressures, reducing engine knock and allowing for a more complete combustion. Approximate values for thermal efficiency in internal combustion can range from 25-45% for gasoline engines and30-50% for diesel engines, depending on the specific engine design, operating conditions and engine speed. However, these values can be impacted by factors such as exhaust gas recirculation, engine load, speed, and engine design features. 4. Explain changes in mechanical efficiency at variable engine load or speed, provide approximate values. Mechanical efficiency is the ratio of useful work output from an engine to the mechanical energy input. It can be affected by several factors including engine load, speed, and design features. At low engine loads and low speeds, mechanical efficiency is typically lower as more energy is lost as heat due to friction in the engine components. It should be noted that with higher engine loads, the mechanical efficiency doesn’t drop down because of the less dependence of this parameter. The higher the speed, the less the mechanical efficiency since the friction losses are greater. 14 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes Approximate values for mechanical efficiency in internal combustion engines can range from 70-90%, depending on the specific engine design, operating conditions, and engine speed. However, these values can be impacted by factors such as engine load, speed, and engine design features. It is important to note that mechanical efficiency and thermal efficiency are interrelated, and changes in one can affect the other. 5. Calculate engine torque and power for given IMEP, mechanical efficiency, swept volume and speed. πΌπΌπΌπΌπΌπΌπΌπΌ = ππ ππππ πππ π ππππ = ππ⋅ππππ = → ππππ = πΌπΌπΌπΌπΈπΈππ ⋅ πππ π ππππ ⋅πΌπΌπΌπΌπΌπΌπΌπΌ⋅πππ π ππ⋅ππ ππ ππππ = ππππ → ππππ = ππππ ⋅ ππππ = ππππ ⋅ πΌπΌπΌπΌπΌπΌπΌπΌ ⋅ πππ π ππ ππππ = ππππ ⋅ ππ = ππππ ⋅πΌπΌπΌπΌπΌπΌπΌπΌ⋅πππ π ππ ππ⋅ππ 6. Calculate specific fuel consumption for given fuel mass flow and power. πΌπΌπΌπΌπΌπΌπΌπΌ = ππππ ππππ 3600 πΉπΉπΉπΉ[ππ/β] = = = ππππ ππππ ⋅ πΏπΏπΏπΏπΏπΏ ⋅ πππ‘π‘β πΏπΏπΏπΏπΏπΏ ⋅ πππ‘π‘β ππππ [ππππ] 7. Calculate thermal efficiency having fuel consumption, lower heating value, swept volume and IMEP. πΌπΌπΌπΌπΌπΌπΌπΌ = ππππ ππππ → ππππ = πΌπΌπΌπΌπΌπΌπΌπΌ ⋅ πππ π πππ‘π‘β = ππππβ = πΏπΏπΏπΏπΏπΏ ⋅ ππππ ππππ πΌπΌπΌπΌπΌπΌπΌπΌ ⋅ ππππ = ππππβ πΏπΏπΏπΏπΏπΏ ⋅ ππππ 8. Draw and explain engine efficiency on specific fuel consumption map. The engine efficiency map, also known as the specific fuel consumption map, is a graph that displays the engine’s thermal efficiency and specific fuel consumption at various engine speeds and loas. The specific fuel consumption map shows the proportion of the energy from the fuel that is converted into useful work. The engine efficiency map provides a visual representation of the engine’s performance under different operating conditions and can be used to identify areas where the engine is operating inefficiently. For example, if the specific fuel consumption is high and thermal efficiency is low at a particular engine speed and load, this indicates that the engine is consuming more fuel than necessary to produce the same power output, resulting in reduced fuel efficiency. 15 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes The engine efficiency map can be used by engine designers and manufacturers to optimize engine performance and reduce fuel consumption, as well as by vehicle manufacturers to choose the most efficient engine for a specific vehicle application. It is also useful tool for fleet managers and operators to monitor engine performance and identify potential areas for improvement. 16 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 6. Fuels 1. Classify fuels according to different criteria. Fuels can be classified according to their physical state as follows: Solid fuels: They exist in a solid state and are found in nature, including coal, wood, peat, and biomass. Liquid fuels: They exist in a liquid state and are usually derived from petroleum, including gasoline, diesel, and fuel oil. Gaseous fuels: They exist in a gaseous state and are often derived from natural gas or petroleum, including propane, methane, and compressed natural gas. They can be also classified regarding the occurrence: Primary fuels: They are derived directly from natural resources and include solid fuels such as coal, wood, and peat, as well as liquid fuels such as crude oil and natural gas. Secondary fuels: They are derived from primary fuels through refinement or conversion processes and include gasoline, diesel, and jet fuel, as well as alternative fuels such as biofuels and hydrogen. 2. Shortly characterise main engine fuels (mineral and renewable). Mineral fuels and renewable fuels are the two main types of engine fuels. Mineral fuels are derived from non-renewable resources, such as petroleum and coal, and are primarily used in internal combustion engines. The main mineral fuels used in engines include gasoline, diesel, and fuel oil. Gasoline is a highly volatile liquid fuel that is used in spark-ignition engines. It is a blend of hydrocarbons and has a high energy content, making it deal for use in automobiles. Diesel is a heavier fuel used in compression-ignition engines. It has a higher energy density than gasoline and is favored for use in heavy-duty vehicles as well as in diesel engines for marine and railway applications. Fuel oil is a heavy residual fuel that is used in large marine and industrial applications, such as power plants and shipping. Renewable fuels, on the other hand, are derived from renewable resources, such as crops, waste, and biobased materials. Renewable fuels are renewable because they are produced from natural, replenishable sources and they can be produced in a matter of months or years rather than millions of years The main renewable fuels used in engines include biofuels, such as ethanol and biodiesel, and hydrogen. Ethanol is a biofuel that is produced from crops, such as corn and sugar sugarcane, and is commonly used in gasoline blends to reduce emissions and increase engine performance. Biodiesel is a renewable fuel that is produced from plant oils, animal fats, and waste grease, and is used in diesel engines as a replacement for mineral diesel fuel. Hydrogen is a zero-emission fuel that can be produced for renewable resources, such as water and wind, and is used in fuel cell vehicles to generate electricity and power the vehicle 17 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 3. Critically evaluate biofuels in aspects of production feasibility, engine compatibility and overall carbon footprint. Biofuels are a type of renewable fuel that have gained popularity in recent years. However, their production feasibility, engine compatibility, and overall carbon footprint are complex and controversial issues that require critical evaluation. First-generation biofuels, such as ethanol and biodiesel, are typically produced from food crops, such as corn, sugarcane, and soybeans. While these fuels have the advantage of being widely available and compatible with existing engines, their production can have a significant impact on food prices and availability as crops that could be used for food production are instead used for fuel production. Additionally, the production of first-generation biofuels requires significant amounts of land, water, and energy inputs, such as fertilizer and pesticides. Second-generation biofuels, such as cellulosic ethanol and algae-based fuels, are produced from non-food crops, such as wood chips and agricultural waste, or from algae. These fuels have the advantage of being produced from non-food crops, which reduces their impact on food prices and availability. However, the production of second-generation biofuels is still in the early stages of development and is more expensive than first-generation biofuels, which limits their viability as a widespread alternative to fossil fuels. Third generation biofuels, such as advanced biofuels and biomethane, are produced from a variety of feedstocks, such as algae, food waste, and agricultural residue. These fuels have the advantage of being produced from a wider range of feedstocks and are typically more energy-efficient than first and secondgeneration biofuels. However, the production of third-generation biofuels is still in the early stages of development and is not yet commercially viable. In terms of engine compatibility, biofuels are generally compatible with internal combustion engines, but there are some concerns about their impact on engine performance and durability. For example, ethanol is highly corrosive and can cause damage to fuel systems, while biodiesel can cause problems with fuel gelling and filter clogging in cold temperatures. The overall carbon footprint of biofuels is a complex and controversial issue, as it depends on many factors, such as the type of biofuel, the source of the feedstocks, and the methods used to produce and transport the fuel. While some studies have found that biofuels can have a lower carbon footprint than fossil fuels, others have found that the carbon footprint of biofuels can be higher, especially when considering the energy and inputs required for their production and transportation. In conclusion, while biofuels offer many advantages, their production feasibility, engine compatibility, and overall carbon footprint are complex and controversial issues thar require further research and analysis. The use of biofuels should be approached with caution, and efforts should be made to improve their production methods and reduce their impact on the environment. 4. Describe chemical composition of gasoline, diesel fuel, natural gas, LGP. Gasoline is a mixture of hydrocarbons, consisting of more than a hundred different compounds. The majority of gasoline is composed of light-to-medium molecular weight hydrocarbons, such as alkanes, alkenes, and aromatic compounds. The exact composition of gasoline depends on several factors, including the source of the crude oil, the refining process, and local regulations, which are increasing share of biocomponents in fuels. Diesel fuel is a mixture of hydrocarbons that is heavier and has a higher boiling point than gasoline. To achieve high cetane numbers, which is a measure of auto-ignition properties, n-alkanes are desirable. Additionally, cetane number increases with the increase of hydrocarbon chains length. 18 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes Natural gas is a mixture of gaseous hydrocarbons, primarily composed of methane, but also containing small amounts of other gases, such as ethane, propane, and butane. Natural gas is typically extracted from underground reservoirs, where it is stored in a gaseous form. LPG, liquified petroleum gas, is a mixture of propane and butane, which are both gases at normal temperatures and pressures, but are stored and transported as liquids. LPG is commonly used as a fuel for heating, cooking, and transportation, as it is easy to transport and store in a liquid form. 5. Provide names and definitions of the main fuel properties. Density: Fuel’s mass per unit of volume. It is temperature dependent and for diesel and gasoline fuel is normally determined at 15 ºC. Density is strongly correlated with other fuel parameters, particularly cetane number, viscosity, and distillation. Viscosity: Fuel’s resistance to flow. It affects the performance of fuel pumps and injection systems. Furthermore, it determines fuel atomization and vaporization. Flash point: It is the lowest temperature at which the vapour above a liquid will ignite when exposed to a flame. It is a measure of both volatility and flammability. Flash point is important primarily from the standpoint of safe handling and storage of fuel. Flash point reflects the volatility of the fuel and is therefore set by distillation parameters. It does not affect engine performance directly. Distillation curve: It is determined by measuring the fraction of a fuel sample removed by heating to progressively higher temperatures. Typically, the curve is characterized by the initial point, which is the temperature of the fuel when the first drop of liquid leaves the condenser. Cloud points: It is the temperature at which a cloud of wax crystal first appears in a fuel sample that is cooled under controlled conditions. The cloud point is determined by visually inspecting a normally clear fuel for a haze. Pour point: It is the lowest temperature at which movement of the fuel sample can be determined when the sample container is titled. Low temperature flow test: It is designed to evaluate whether a fuel can be expected to pass through an engine fuel filtration system. Cold filter plugging point: It is like the LTFT test. It provides a close correlation with vehicle operability limits. Vapour pressure: It is defined as the pressure exerted by a vapor in thermodynamic equilibrium with liquid at a given temperature in a closed system. For some fuels like LPG or DME it is important from the storage point of view. Such fuels under ambient temperature must be kept in pressurized containers where two fractions are presented. Heating value: Actually, two heating values are in common use: the higher or gross heating value and the lower or net heating value. Both quantities are measured using a calorimeter that measures the heat transfer from the hot combustion gases as they are cooled to the initial temperature of the reactants. The higher heating value assumes that all the water in the products is condensed liquid while the lower value assumes that all the water is present as vapour. The lower heating value is normally used for engine applications because water in exhaust is in a gas state. The simplest way of LHV calculation is summarizing heating values of elements, multiplied by their mass fractions. Heating value of a fuel is defined as the total heat produced when a unit of mass of fuel is completely burnt with pure oxygen. When water is present in the flue gases, the heating value is said “higher heating value”. If the water is present in the liquid form, it is said “lower heating value”. 19 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes Theoretical air requirement: It is known as the stoichiometric air requirement. Theoretical air demand for fuel can be calculated if fuel composition is known. Cetane number: The cetane number of a fuel is a standardized measure of the fuel’s ignition quality, specifically, the ignition delay time of a diesel fuel in comparison to that of pure cetane (hexadecane). A higher cetane number indicates a shorter ignition delay, meaning quicker and smoother combustion in a diesel engine. The cetane number typically ranges from 40 to 55 for commercial diesel fuels. Octane number: The octane is a measure of the performance of a fuel. The higher the octane number, the more compression the fuel can withstand before detonating. Fuels with a higher-octane number can be used in higher compression ratios. 6. What is lower/higher heating value and how this parameter can be calculated? Roughly calculate heating values for fuels with given chemical formula (e.g. propane C3H8) or composition (given C, H, 0). The heating value is defined as the total heat produced when a unit of mass fuel is completely burnt with pure oxygen. When the water is present in the flue gases, the heating value is said “Low heating value”. If the water is present in the liquid form, it is said “lower heating value”. The heating value can be calculated by balancing the standard heat of formation of the substances participating in combustion. The simplest way of LHV calculation is summarizing heating values of elements, multiplied by their mass fractions: πΏπΏπΏπΏπΏπΏ = 0.022 + 33.94ππ − 0.1ππ + 103.3β [ππππ/ππππ] 3 ⋅ 12 = 0.23 3 ⋅ 12 + 7 ⋅ 16 + 8 7 ⋅ 16 = 0.72 ππ = 3 ⋅ 12 + 7 ⋅ 16 + 8 ππ = β= 8 = 0.05 3 ⋅ 12 + 7 ⋅ 16 + 8 πΆπΆ3 π»π»8 + 5ππ2 → 3πΆπΆππ2 + 4π»π»2 ππ πΏπΏπΏπΏπΏπΏ = 0.022 + 33.94 ⋅ 0.23 − 0.1 ⋅ 0.72 + 103.3 ⋅ 0.05 = 12.92 ππππ/ππππ 7. Calculate mass-based theoretical air requirements of fuel for given chemical formula or composition. (In case of propane) πΆπΆ3 π»π»8 + 5ππ2 → 3πΆπΆππ2 + 4π»π»2 ππ For every propane mol, 5 oxygen mol are requested: 1000 ππ πΆπΆ3 π»π»8 ⋅ 1 ππππππ πΆπΆ3 π»π»8 5 ππππππππ2 32 ππππ2 100 ππ ππππππ ⋅ ⋅ ⋅ = 17.32 ππππ ππππππ 44 ππ πΆπΆ3 π»π»8 1 ππππππ πΆπΆ3 π»π»8 1 ππππππ ππ2 21 ππ ππ2 For each kg of air, 17.32 kg of air will be requested. 8. Calculate volume-based theoretical air requirement of fuel for a given chemical formula (e.g., methane, propane, ethanol, methanol, DME (CH3-O- CH3)). 1000 ππ πΆπΆ3 π»π»8 ⋅ πΆπΆ3 π»π»8 + 5ππ2 → 3πΆπΆππ2 + 4π»π»2 ππ 1 ππππππ πΆπΆ3 π»π»8 5 ππππππππ2 32 ππππ2 100 ππ ππππππ 1 ππ3 ππππππ ⋅ ⋅ ⋅ ⋅ = 14.20 ππ3 ππππππ 44 ππ πΆπΆ3 π»π»8 1 ππππππ πΆπΆ3 π»π»8 1 ππππππ ππ2 21 ππ ππ2 122 ππ ππππππ 20 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 7. Engine Exhaust Composition 1. Calculate exhaust composition for stoichiometric mixture of fuel with known molecule or composition. Let’s use Biodiesel C11H21O2 in diesel: πΆπΆππ π»π»ππ ππππ + ππ(ππ + 0.25ππ − 0.5ππ)(ππ2 + 3.76ππ2 ) → ππππππ2 + 0.5πππ»π»2 ππ + (ππ − 1)(ππ + 0.25ππ)ππ2 + 3.76ππ(ππ + 0.25ππ − 0.5ππ)ππ2 %ππ2 = %ππ2 = πΆπΆ11 π»π»21 ππ2 + 13.325 ππ2 + 50.102 ππ2 → 11πΆπΆππ2 + 10.5π»π»2 ππ + 50.102 ππ2 + 4.875ππ2 4.875 = 7.4% 11 + 50.102 + 4.875 50.102 = 75.9% 11 + 50.102 + 4.875 %πΆπΆπΆπΆ2 = 11 = 16.7% 11 + 50.102 + 4.875 2. List toxic exhaust components emitted by IC engines. The toxic components emitted by internal combustion engines include: Unburnt hydrocarbons (UHCs). Nitrogen Oxides (NOx). Carbon monoxide (CO). Sulphur oxides (SOx). Particulate matter (PM). 3. Provide approximate exhaust composition of spark ignition or diesel engine. Approximate exhaust composition for SI engines: Approximate exhaust composition for diesel engines: Carbon Oxide (CO2): 14-17% Oxygen (O2): 0-2% Nitrogen (N2): 75-80% Water vapor (H2O): 5-10% Carbon monoxide (CO): 0-1% Unburt hydrocarbons (HC): 0-2% Carbon Oxide (CO2): 14-20% Oxygen (O2): 0-2% Nitrogen (N2): 70-80% Water vapor (H2O): 5-10% Carbon monoxide (CO): 0-2% Unburnt hydrocarbons (HC): 0.05-1% 4. Describe changes in diesel engine exhaust composition at variable load At variable load conditions, the exhaust composition of diesel engine can change due to changes in engine operating parameters such as fuel-air ratio, combustion temperature and pressure, and engine speed. At lower loads, the engine operates at a leaner air-fuel ratio, which reduces the amount of carbon monoxide (CO) and unburnt hydrocarbons (HC) produced but increases the amount of nitrogen oxides (NOx) produced. At higher loads, the engine operates at a richer air-fuel ratio, which increases the amount of carbon monoxide (CO) and unburnt hydrocarbons (HC) produced but reduces the amount of nitrogen oxides (NOx) produced. 21 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes The amount of particulate matter (PM) produced may increase at higher loads due to incomplete combustion, while the amount of carbon monoxide (CO2) and water vapor (H2O) produced is largely independent of engine load. 5. Describe sources of unburnt hydrocarbons emissions. Unburned hydrocarbons emissions are caused by incomplete combustion of fuel in an internal combustion engine. There are several sources of unburned hydrocarbons in internal combustion engines, including: Poor fuel-air mixing: If the fuel and air are not mixed well before entering the combustion chamber, some fuel will not be burned and will be expelled as unburned hydrocarbons. Insufficient ignition timing: If the ignition timing is set too late, the fuel will not be fully burned before the exhaust stroke, leading to unburned hydrocarbons in the exhaust. Fuel quality: Poor fuel quality, such as dirty or contaminated fuel, can also contribute to unburned hydrocarbons emissions. 6. Describe sources of CO emission. The sources of CO emissions from an IC engine can be traced back to several factors including: Insufficient oxygen: If the engine is not receiving enough oxygen, the fuel-air mixture will not burn completely, resulting in the formation of CO. Lean air-fuel mixture: A lean air-fuel mixture, where there is not enough fuel in relation to the amount of air, can also result in incomplete combustion and the formation of CO. Incomplete combustion: If the fuel air-mixture does not ignite uniformly or the combustion process is interrupted, CO can be formed. High combustion temperature: High combustion temperatures can lead to CO formation as the fuelair mixture may not have sufficient time to react completely before the exhaust stroke. Engine design: Engine design factors such as carburettor size, valve timing, and compression ratio can also affect the formation of CO. 7. Describe conditions for NOx formation. There are several reasons of NOx emissions. It occurs under high temperatures and pressures, such as those found in the combustion chamber during the engine’s power stroke. Factor that contributes to high temperature and pressure conditions include High engine operating temperatures, high air-to-fuel ratios, high combustion chamber temperatures, high cylinder pressure, and long duration of combustion. 8. Describe process of particulate matter formation Particulate matter (PM) is formed from the incomplete combustion of fuels, leading to the formation of solid or liquid particles in the exhaust. The process of PM formation in internal IC engines includes the following steps: Fuel droplets evaporate and mix with air. The mixture burns, creating high temperature and pressure. Soot particles are produced from the incomplete combustion of the fuel mixture. Cooling of the exhaust gases condenses the soot particles into larger PM. Additional PM can be formed from lubricating oil, wear of engine components, and other sources. 22 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 9. What physical properties of exhaust compounds are utilised for measurement of their concentrations. Exhaust gas concentrations are measured using different analytical techniques, which utilize different physical properties of the compounds present in the exhaust. Some of the commonly used physical properties include: Infrared Absorption: Concentrations of gases such as carbon monoxide, carbon dioxide, and nitrogen oxides can be determined by infrared absorption spectroscopy. Thermal conductivity: The thermal conductivity of a gas mixture is proportional to tis composition, which can be used to measure concentrations of various gases. Flame Ionization: The conductivity of a flame is proportional to the concentration of hydrocarbons present in the sample. This principle is used in flame ionization detectors to measure the concentration of s sample. It can be used to measure the concentrations of various exhaust compounds. 10. Which fuel and engine properties affect CO2 emission. The properties of the fuel directly impact CO2 emissions include: Carbon content: Fuels with a higher carbon content release more CO2 when burned, as more carbon is converted to CO2 during combustion. Energy content: More energy-dense fuels, such as gasoline and diesel, release more CO2 per unit of energy produced, as more fuel is burned to produce the same power output. Octane: Fuels higher octane number tend to have lower CO2 emissions, as they burn more efficiently and generate less waste heat. Sulfur content: Sulfur in fuels can cause corrosion and reduce the efficiency of catalytic converters, indirectly affecting CO2 emissions. Renewability: Renewable fuels, such as biofuels and hydrogen, can reduce CO2 emissions, as they do not release new carbon into the atmosphere and may displace the use of fossil fuels. 11. Calculate CO2 emission for given composition and fuel consumption. πΈπΈπΆπΆππ2 = πΉπΉπΉπΉ ⋅ ππ ⋅ 23 44 12 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes 8. Hybrid electric vehicles 1. Provide definition of hybrid power train. A hybrid powertrain is a system used in vehicles that combines two or more sources of power, such as conventional internal combustion engine and an electric motor, to power a vehicle. The primary aim of a hybrid powertrain is to improve fuel efficiency and reduce emissions by optimizing the use of the different power sources and reducing the need for the internal combustion engine to run at its most fuel-intensive power levels. In a hybrid powertrain, the internal combustion engine and electric motor work together, with the electric motor providing additional power when needed and the internal combustion engine providing power when the battery is depleted. The two power sources can also be used to recharge the battery. 1. 2. 3. 4. 5. 2. List few types of power sources used in hybrid powertrains. Internal combustion engine (ICE). Electric motor/battery. Solar panels. Fuel cells. Regenerative braking systems. 3. Explain the idea of hybridization – indicate how energy efficiency is increased. Hybridization refers to the concept of combining two or more technologies to create a more efficient system. In the context of energy, hybridization can refer to the combination of different energy sources (such as renewable and non-renewable) and/or the integration of different energy storage technologies. By combining different technologies, energy efficiency can be increased as it provides a more flexible and reliable energy supply. For example, the integration of renewable energy sources with traditional energy sources can reduce the dependence on non-renewable energy sources are not available. Additionally, combining different energy storage technologies can provide a more efficient means of storing and using energy. 4. List and explain benefits from hybridization. Reduced engine dimensions: Hybrid powertrains can reduce the size of the IC engine, as the electric motor can provide additional power and support the engine. High torque at low speeds: Electric motors can provide high torque at low speeds, improving acceleration and overall performance of the vehicle. Improved fuel economy: The use of both an IC engine and electric motor in a hybrid powertrain can improve fuel economy by reducing the amount of work required from the engine and increasing the efficiency of energy use. 24 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes Enhanced regenerative braking: In hybrid systems, the electric motor can act as a generator during regenerative braking, converting the energy generated during braking into electrical energy that can be stored in the battery. Improved emissions: Hybrid systems can reduce emissions by improving fuel efficiency and allowing the vehicle to operate in electric-only mode, reducing or eliminating tailpipe emissions. Reduced noise and vibration: The electric motor in a hybrid system can provide additional power at low speeds, reducing the need for the internal combustion engine to work as hard and reducing noise and reducing noise and vibration. Increased power: The combination of an IC engine and electric motor in a hybrid system can provide increased power and performance compared to traditional IC engine vehicles. 5. List and define different stages of hybridization. 1. Mild hybrid: A mild hybrid system includes a small electric motor and battery that supports the IC engine, improving fuel efficiency and reducing emissions. The electric motor is not powerful enough to drive the vehicle on its own and the IC engine remains the primary source of power. 2. Full hybrid: A full hybrid system includes a larger electric motor and battery that can power the vehicle in electric-only mode and also support the IC engine. The electric motor can provide additional power during acceleration and improve fuel efficiency. 3. Plug-in hybrid: A plug-in hybrid system is similar to a fully hybrid, but it also includes the ability to recharge the battery through an external power source, such as a wall outlet. This allows for extended electric-only driving range and improved fuel efficiency. 4. Fuel cell hybrid: A fuel cell hybrid system includes a hydrogen fuel cell that provides power to an electric motor, with an additional battery to store energy generated during regenerative braking. This type of hybrid system has zero tailpipe emissions and improved fuel efficiency compared to traditional IC engine vehicles. 6. Describe in detail and draw design of different hybrid powertrains (parallel, series, series-parallel, slit axle, split power). Provide pros and cons. A parallel hybrid powertrain combines an IC engine and an electric motor that can both power the vehicle independently or work together to provide additional power Pros: Disadvantages: ICE operation point moves to the region higher efficiency Low power of electric motor Additional power from the electric motor Lack of electric only propulsion Start-stop function Low efficiency of regenerative braking 25 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes A series hybrid powertrain is a type of HEV system where the ICE and electric motor are combined in such a way that the ICE does not directly power the wheels. Instead, the ICE acts as a generator, producing electricity to power the electric motor which in turn propels the vehicle. Pros: Cons: Possibility to switch off ICE Large weight and dimensions Effective regenerative braking Low efficiency High torque at low speeds A series-parallel hybrid powertrain is a type of HEV that combines the benefits of both series and parallel hybrid systems. In a series-parallel hybrid powertrain, the ICE and electric motor can work together to drive the wheels, or the electric motor can work alone to drive the wheels. The ICE and electric motor can also work in series to charge the battery and provide additional power to the wheels Pros: Cons: Possibility to ICE switch off. Lack of fluent control of ICE speed and load Larger power of electric motor. When both energy converters are used. Moderate efficiency of regenerative braking 26 Máquinas Marinas y Sistemas de Propulsión 1 Apuntes Split-axle hybrid powertrains refer to hybrid systems in which the ICE and electric motor are located on separated axles. The power from each source is sent to the wheels independently, allowing for improved traction and efficiency. Pros: Cons: Improved traction Lack of possibility to switch off the drives Better weight distribution Low efficiency of regenerative braking More space for battery pack Lack of start-stop function. A split power hybrid powertrain is a type of hybrid vehicle in which the internal combustion engine and electric motor are connected through a power split device, such as a planetary gear set. The power split device allows for the power from the internal combustion engine and electric motor to be distributed between the wheels and to the battery for changing. Pros: Cons: Fluently variable gear ratio Continuous operation of all devices Lack of clutches 27
