Contents Perform test of an internal combustion engine ........................................................................................... 1 Objective ....................................................................................................................................................... 1 Brief Theory................................................................................................................................................... 1 Experimental procedure ............................................................................................................................... 2 ...................................................................................................................................................................... 4 Calculations ................................................................................................................................................... 4 Methodology................................................................................................................................................. 7 Conclusions and discussion ........................................................................................................................... 8 References .................................................................................................................................................... 8 Perform test of an internal combustion engine Objective A method of testing an internal combustion engine to detect engine defects. After the engine has been assembled, the engine is cranked, gas under pressure is injected into the intake ports, and the pressures developed at the exhaust ports as the engine is cranked are noted and evaluated. The pressurized air injected into the intake ports amplifies the pressure signals developed at the exhaust ports so as to provide more accurate identification of engine defects and detect engine defects that might go undetected utilizing prior art technology. Brief Theory Internal combustion engine is the most spread motor machine in the world. The present work shows an alternative perspective to the study of the work cycle of combustion engines. This is not obtained by direct measurement, but is built with the data obtained in two experimental tests. In the first, pressure variations without combustion are measured in one cylinder of the engine, while the engine is fully loaded with the remaining cylinders. Then, during a traditional brake power test, the combustion products are measured to obtain the data corresponding to the combustion and expansion phase by calculation, applying the model of the indicated cycle provided to the same number of rotations as in the first test. As an application of the principle of overlapping effects, the result is obtaining the indicated cycle of the machine that serves to evaluate its efficiency. At the same time, the actual working fluid and the particular system are characterized. The text that is presented below focuses on the experimental validation of the described trials, presenting the methodology followed from the metrological and statistical point of view. It is expected that the results of the application of the model of the indicated cycle will provide data to characterize alternative hybrid fuels to be used in existing engines. The indicated cycle of an internal combustion engine is the most usual tool used to obtain the work of the cycle and the indicated power of the machine. The work performed by the fluid that evolves in the machine is called indicated power. With the engine in test phase, the indicated power is the reference against which the mechanical performance of the motor is determined. In this article we will illustrate a practical example of how the data obtained in different tests of a four-stroke spark ignition engine are processed for the application of the indicated cycle model provided in an existing engine. The indicated cycle provided is a way to obtain the open cycle of the pressures of an internal combustion engine, without measuring the entire development of the pressures inside the cylinder directly. Although its execution is more laborious, its implementation with industrial sensors of current use lowers the equipment costs in a remarkable way. It is obtained as an application of the concept of superposition of effects, where the cycle is composed of the data provided by different tests performed at the same regime of rotations and full load. Experimental procedure The test is performed on a hydraulic dynamometer bench that opposes a torque resistant to the driving torque generated by the combustion engine. The test is carried out at different rotation speeds, and in each case the pressures in the cylinder n°4 of the open cycle without combustion is obtained, while the engine runs at 100% load on the remaining three cylinders. To register the pressure, a Danfoss model MBS 3000 analog sensor with proportional current output signal type 4 - 20mA is used. A position sensor is used to register the piston passage through the top dead center (TDC), placed on the crankshaft pulley. This sensor allows determining the start and end of each operating cycle. A Siemens model 3RG4075 - 0AJ00 inductive proximity sensor is used for this task. Both sensors are connected to individual channels of a GW Instek GDS -2062 digital oscilloscope. Digital oscilloscope screen shot. In yellow, channel 1 register the data from the pressure sensor. In green, channel 2 shows the TDC sensor. (b)Pressure sensor installed in the motor. The oscilloscope screenshot when measuring the 2290 rpm series. Once the experimental register has been obtained, the data is transferred to the spreadsheet for first analysis. This consists on determining the good measurements that will intervene in the most representative cycle calculation, and establishing with precision the rotation regime at which the test was carried out. Conserving only the complete cycles comprised between the TDC marks and counting the number of complete cycles in the time interval in which they have been recorded, the number of rotations to which the test was actually performed can be accurately established. Once the rotation regime has been established for each series of data and the number of cycles that make up each series, it is necessary to establish the most representative cycle of each events series. To do this, the x-axis it is changed to indicate degrees of crankshaft rotation instead of time; and the y-axis to indicate pressure instead of voltage, and all the events that make up each series are superimposed. For the present article, we have chosen to work with the measurements obtained at 2715 rpmthat is very close to the number of rotations where the engine has the maximum torque. Calculations Fuel Consumption Fuel volume flow is figure out by using drained fuel volume and its drain time. As fuel volume flow is find out we can find fuel mass flow rate by multiplying it with its density. Air Consumption Air mass flow rate can be finds by using coefficient of discharge, diameter of orifice, Gas constant, ambient pressure and pressure difference between orifice and by using ambient temperature. All these are put in formula to find air mass flow rate Brake Power By multiplying angular velocity and torque brake power is figure out. While angular velocity is calculated by using speed multiply with pie and 2 and then divide by 60. Specific Fuel Consumption From fuel mass flow rate and brake horse power specific fuel consumption is finds out. Fuel mass flow rate is multiples with 3600 and then divide with the ratio of brake power and 1000. Air Fuel Ratio By dividing air mass flow rate to fuel mass flow rate air fuel ratio is calculated. Heat energy by Combustion Fuel mass flow rate is multiple with calorific value to find combustion energy. Inlet Air Enthalpy Air mass flow rate is multiple with specific heat at constant pressure and ambient temperature to finds out inlet air enthalpy. Thermal Efficiency Brake power is divides by the multiple fuel mass flow rate and calorific value to calculate thermal efficiency. Volumetric Efficiency Volumetric efficiency is calculated by multiple of 100 and division of measured volume and calculated volume. Calculated volume is the ratio of multiple of engine capacity and speed and multiple of half of stroke and 60. While measured volume is the multiple of air mass flow rate, gas constant and ambient temperature and divides by ambient pressure. Brake Mean Effective Pressure It is calculated by division of multiple of 60, brake power and half of stroke to multiple of 0.1, speed and engine capacity. Methodology For the first test, a pressure sensor will be installed in the spark plug hole, corresponding to the cylinder number four. The engine will compress the working fluid, composed by the mixture of air and gasoline provided by the carburetor or injection system. Since the cylinder number four spark plug is missing, the mixture will not ignite, allowing its expansion and exit through the exhaust pipe. All these events will be registered by the pressure sensor. This situation is illustrated in Figure 1 with a full line and we will call it the indicated cycle without combustion. This test will allow obtaining the real pressure variation curve for the engine intake and compression races, depending on the angle of rotation of the axle. The effect that the combustion process has on the indicated cycle can be seen in figure 1 in broken lines. To obtain the value of the maximum combustion pressure, a second test will be carried out, also at full load and at the same rotation regime, in which the specific fuel consumption of the engine and the elemental composition of the combustion gases will be determined. With the help of the combustion products enthalpy diagram, the temperature and pressure values corresponding to the maximum pressure developed by the cycle will be obtained. The expansion curve will be modeled with the average polyropic coefficient in the expansion phase taking as reference the maximum combustion pressure and the final pressure in that phase observed in the previous test. Open cycle of an SI-FSE motor. The cycle without combustion phase is shown in continuous line. The combustion effect is shown in broken line. A third test consisting of a traditional brake power test was also carried out in order to obtain the characteristic power curve of the engine. This test is not part of the indicated cycle provided scheme, but is obtained in order to allow the engine mechanical performance calculation, useful to establish the method validity. For the basic relationship between the degrees of rotation of the motor shaft and the volumes observed inside the cylinder should be established at first. This is obtained from the geometric analysis of the crankshaft-rod system: 𝑉𝑉𝑥𝑥=𝑆𝑆.�𝑟𝑟.(1−𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐)+𝑟𝑟 𝜑𝜑.�1−�1−𝜑𝜑2𝑐𝑐𝑠𝑠𝑠𝑠2𝑐𝑐��+𝑉𝑉2 (1)Where Vx represents the volume inside the cylinder for each angle α of the motor shaft rotation. The r parameter is the crank radius, φ is the crankshaft turning ratio equal to the ratio between r and the l length of the connecting rod between centers. S is the cylinder cross section surface of and V2 is the combustion chamber volume. Adopting the ideal gases model, the polytropic compression curve (in this case obtained experimentally) is: 𝑃𝑃𝑦𝑦= 𝑃𝑃1�𝑉𝑉1 𝑉𝑉𝑥𝑥�𝑠𝑠𝑐𝑐 (2)Where the value Py results the pressure corresponding to the volume Vx inside the cylinder, in reference to V1 (cylinder total volume), and the pressure P1 at the beginning of the compression phase. The exponent nc is called the average polytropic coefficient, and in addition to defining the shape of the compression curve, from the thermodynamic point of view, it defines the heat losses of the system. As the compression curve is known, nc values can be obtained for each volume (any volume) Vx.In a real compression, the polytropic pressure increase can only be considered to the point where the fuel mixture ignites, that situation does not occur when the cylinder volume is V2, but in the volume corresponding to the ignition advance, which will be called V2´. In all cases V2´ ˃ V2. The nc value does not remain constant, but varies throughout the stroke. However, the nc coefficient can be taken as a Conclusions and discussion The method consisting on obtaining the indicated cycle of the engine as the composition of a pressure diagram without combustion phase, plus a power phase modelled with the data obtained from a second brake power test, with the same state of load and speed rotation, seems possible. This is shown by the value obtained from mechanical performance, which, although high, is within the expected values. I n its practical execution, the experimental method is laborious, but from the point of view of the necessary equipment, it is extremely economical since the sensors and instruments used are of common use in industrial applications. The indicated work calculated with the integration method of the compression and power polytropic function, using the average polytropic exponent for the whole stroke, is more accurate than other theoretical methods. Even, when the air and fuel mixture, is considered as an ideal gas. Likewise, the information obtained with the pressure sensor during the intake and compression strokes allow plotting with precision the curve of real variation of polytropic coefficient in those phases, at the same time that conclusions and valuable characterizations about the working fluid can be obtained. The polytropic compression coefficient values also findsimilarity with the values usually registered in the specialized literature. References Caputo, D.C.,Berberi, R.O.,Ferré, N.A., Russo, F.G.,Receloglu, G.A., Cavataio, P.G., Bruno, J.M. (2017).Determinación experimental de la variación del coeficientepolitrópico de compresiónutilizandodiagramasabiertos. Ciencia y Tecnología 17, pp. 9-28. Jovaj, M.S. (1982). Motores de automobile. Ed. Mir, Moscú. Lapuerta, M. (2002).Study of the compression cycle of reciprocating engine through the polytropic coefficient. Elsevier Science Ltd, Valencia. Nieto Garzon, N., MenesesZarza, H., Schroeder, F., Dos Santos, R., Oliveria, A.M. Bazzo, E (2016). Aplicação de procedimentos estatísticos na análise da curva de pressão na câmara de combustão de motores de ignição por compressão. Jornadas Iberoamericanas de Motores Térmicos y Lubricación, 30 august –1 September 2016, La Plata, Buenos Aires. Torregosa, A.J.,Olmeda, P. (2011). Pérdidas de calor. Refrigeración. En: Payri, F. y Desantes, J.M. (ed.) Motores de combustion