Thermomachines TRMMCA4 / TRM4A11
1st semester 2022
2022-05-06: Week 9 part 1
RICE cycles
Fuel- and induction systems
Pulkrabek pp. 213 – 225, Section 5
• Fuel injector (Figure 9.1, with animation)
• Mechanical- and electronic fuel injection
 Mechanical: Bosch K-Jetronic, 1973 – ‘95 (Figure 9.2)
 Digitally controlled injection: Bosch LH-Jetronic, 1982 – ’98
(Figure 9.3)
• Multipoint port injection (Figure 9.4)
• Direct injection systems for SI engines, “GDI” (Figure 9.5)
• Combination of direct- and indirect injection system (Figure 9.6,
not in textbook)
• Throttle-body injection systems (Pulkrabek pp. 220 – 223)
• Diesel injection systems (Figure 9.7, Pulkrabek pp. 246 – 250)
2022-05-06: Week 9 part 1
(continued)
RICE cycles
Fuel- and induction systems (continued)
Dual-fuel systems (Pulkrabek pp. 239 – 240, Section 8)
Induction for two-stroke cycle engines
(Study Pulkrabek pp. 241 – 246, Section 9, including Example
Problem 8)
Engine charging
Supercharging (today’s lecture, Pulkrabek pp. 234 – 236,
Section 7)
Turbocharging, intercooling, compound charging 23 April
Fuel systems
Figure 9.1: Fuel injector cutaway
Animation
http://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gif
Mechanical petrol injection
• Mechanical injection is the oldest and simplest injection
system type on SI engines
• Introduced around WWII on German fighter aircraft
engines, it allowed them to fly upside down without
starving the engines of fuel
• In the 1950s Bosch started developing mechanical
injection for Mercedes Benz racing cars
• It was introduced on production cars in the 1960s (e.g.
BMW, MB, Porsche)
Mechanical petrol injection
An example of a mechanical injection system is Bosch
K-Jetronic, shown in Figure 9.2
It was used in various SI engines from 1973 to 1995
• It injected fuel continuously and in bulk into the intake manifold,
just upstream of the intake valve, where the air and fuel mixed
• It was therefore an indirect injection system
• The mixture in the manifold was drawn into a cylinder when the
intake valve of that cylinder opened
• The system had a small number of sensors
• It gave better engine output and fuel economy than carburettors
Bosch developed it into more advanced systems like L-, LEand LH-Jetronic
Further development of electronic systems (e.g. Motronic)
made it obsolete
Figure 9.2: Mechanical petrol
injection system (Bosch K-Jetronic)
Source: http://america.pink/jetronic_2221987.html
Digitally-controlled petrol injection
An example of a digitally-controlled injection system is
Bosch LH-Jetronic, shown in Figure 9.3
• It was introduced on Volvo 240 engines exported to
California in 1982, and was produced until 1998
• It had more sensors than K-Jetronic
• LH-Jetronic measured intake airflow by means of a hotwire anemometer
• An ECU calculated the opening period of the injectors,
thereby determining the required fuel mass flow
• Microcontrollers by Intel and Siemens were used in the LH
2.2 and LH 2.4 versions respectively
• LH 2.4 also had adaptive l-control and fuel enrichment
based on exhaust temperature
• Post-1995 versions had immobiliser functions
Figure 9.3: Digitally controlled petrol
injection system (Bosch LH-Jetronic)
Source: “Machine Design,” 23 August 1990, p. 82
Multipoint port petrol injection
Multipoint port injection (“MPI”) injects petrol into the
intake ports just upstream of each cylinders intake valve
(see Figure 9.4). MPI is an indirect injection system.
Three major types exist, i.e.
• Simultaneous injection: All the fuel injectors simultaneously
inject the same mass of fuel into the intake of each cylinder.
Injection is not timed.
• Batched injection: The fuel is injected into the intake ports
of a number of cylinders in groups. As with simultaneous
injection, injection is not timed.
• Sequential injection: Injection coincides with every cylinders
air intake. Most modern engines use sequential injection.
Direct injection systems already appearing in numbers on
production cars are replacing it.
Figure 9.4: Multipoint point port
petrol injection
Source: http://www.emeraldm3d.com/articles/injection-systems/
Direct petrol injection systems
Gasoline direct injection (“GDI”)
• Direct injection is a highly advanced electronic system,
injecting fuel directly into the combustion chamber, under
high pressure.
• The air and fuel do not mix in the intake duct, but in the
combustion chamber, when the intake valves are already
closed. This allows more air to be drawn into the cylinder, as
well as more fuel to be injected.
• During injection, the cylinder walls and piston crowns are
cooled, permitting higher compression ratios.
• Some systems use piezoelectric injectors, with quick
response that makes multiple injections possible during one
cycle.
• Almost no fuel is present in the intake duct, causing more
complete combustion.
• The result is higher engine torque and power output, leaner
FA mixtures, improved efficiency and lower emissions.
• It was combined with engine charging during the previous
decade, thereby further improving engine efficiency.
Direct petrol injection systems
Gasoline direct injection (“GDI”)
A schematic of a GDI system is shown in Figure 9.5. The
system is more complex, with a larger number of sensors
in particular, than any of the systems shown before.
Sensors include
•
•
•
•
•
•
•
•
•
•
Throttle position sensor
Crankshaft- and camshaft angular position sensors
Crankshaft speed sensor
Intake air massflow and -temperature sensors
Intake manifold sensor
Injector fuel pressure sensor
Cooling water temperature sensor
Knock sensor
Exhaust temperature sensor
Various exhaust gas oxygen sensors
Figure 9.5: Direct fuel injection with
electronic control (Bosch)
Source: http://us1.webpublications.com.au/static/images/articles/i1078/107830_10lo.jpg
Combined direct- and indirect petrol
injection systems
A combined direct- and indirect injection system
schematic is shown in Figure 9.6
This type of system is mainly used by VW and Toyota
Operation
• Direct injection into the combustion chamber at extremely high
pressure during startup and at high loads
• Indirect injection (“MPI”) at low pressure into the manifold at
part load
Results (claimed by Audi)
Improvement in fuel consumption by 21% over the corresponding
direct injection engine, and a further reduction in emissions,
meeting the most stringent Euro 6 standard (Audi 1,8 TFSi)
Figure 9.6: Combination of directand indirect petrol injection
Source: http://bioage.typepad.com/.a/6a00d8341c4fbe53ef01a3fc33785b970b-popup
Dual-fuel engines
Read Pulkrabek pp. 239 – 240, Section 8
Intake for two-stroke cycle engines
Study Pulkrabek pp. 241 – 246, Section 9, including
Example Problem 8
Intake for CI engines
Read Pulkrabek pp. 246 – 250, Section 10
Summary
Diesel engines don’t need throttles (some of them, e.g. MB 320
CDI) have throttles. Their load demand is simply met by the
correct fuel supply. This was discussed in the lectures of
week 6 part 2 slides 17 & 18.
The intake system is designed with very little flow restriction.
This gives high volumetric efficiency at all engine speeds. Also,
fuel is added late in the compression stroke, after completion of
the intake stroke, which further improves volumetric efficiency.
Most modern CI engines are turbocharged, which enhances air
intake even more.
Combustion continues well into the power stroke. Fuel with the
correct cetane number must be used so that self-ignition
initiates the start of combustion at the proper piston position.
Intake for CI engines
Injection pressure must be higher than for SI engines. The
cylinder pressure is very high near the end of the compression
stroke, due to the high compression ratios of CI engines.
Orifice hole diameter of injectors is typically in the range of
0,2 mm to 1,0 mm. Mass flow rate of fuel through an injector is
given by Pulkrabek p. 247 Equation (27), while the total mass
injected by an injector is given by Equation (28). Pressure
difference across the injector is approximately equal to injection
pressure. It is desirable that the crank angle of rotation through
which injection takes place be almost constant for all speeds.
To this end, injection pressure must be proportional to engine
speed squared.
Modern “common rail” Diesels use piezo-electric injectors with
fuel pressures up to 1 800 atm. A modern injector spraying
Diesel fuel into a combustion chamber (a cavity in the piston
crown) is shown in Figure 8.22.
Figure 9.7: Injector spraying Diesel
fuel into combustion chamber
Source: http://assets.hemmings.com/story_image/70176-500-0.jpg?rev=2
Throttle-body petrol injection
systems
Read Pulkrabek pp. 220 – 223, Section 5
Engine charging
Supercharging and turbocharging
Pulkrabek pp. 234 – 239 , Section 7
“Superchargers and turbochargers are compressors
mounted in the intake system and used to raise the pressure
of the incoming air. This results in more air and fuel entering
each cylinder during each cycle. The added fuel and air
create more power during combustion, and the net (torqueand) power outputs of the engine are increased”.
A comparison between naturally aspirated- and
turbocharged engine output is shown in Pulkrabek p. 234,
Figure 18.
Engine charging
Supercharging and turbocharging
(The torque outputs of turbocharged- and unblown engines
were mentioned in the slides of week 7 part 1. The 4cylinder 2 l turbocharged VW / Audi engine had a brake
specific torque of 200 Nm/l, while that of the 6-cylinder 3,4 l
unblown Porsche Cayman S engine was 109 Nm/l).
Supercharging is discussed today. Turbocharging will be
covered in more detail in a later lecture.
Supercharging
• A supercharger is a positive displacement compressor
mounted in the engine intake system, upstream of the
intake valves
• It improves engine power
• It is mechanically driven by the engine, from the crankshaft
• Its rotational speed is directly proportional to that of the
engine
• It has good throttle response at low engine speeds and
-loads, i.e. no “lag”
• However it drains engine power
(see Pulkrabek pp. 238 – 239, Example 6)
• Its drive also has losses, i.e. parasitic engine losses
• It is bulky, expensive and noisy
Supercharging
(continued)
• Superchargers are not as efficient as turbochargers ito
energy consumption and generally do not improve fuel
economy
Superchargers
[Stone, 1987]*
Types of superchargers (Stone, 1987)*
• Roots blower
• Vane compressor
• Screw compressor
Schematics of the three types are shown in Figure 9.10,
from Stone (1987)*
*
Stone, R., “Introduction to Internal Combustion Engines,” 2nPrint, Macmillan, London, 1987
Figure 9.10
Supercharger types [Stone, 1987]*
Examples of supercharged engines
• Mercedes Benz “Kompressor” engines
• Audi S4 engine (2008 – 2016)
• Jaguar XJ-R V8 engine