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In this paper, a generic methodology is proposed to simulate the static and dynamic responses of a SI gas engine. The predicted simulation of engine performances is based on a one zone thermodynamic model. The turbocharger is modeled by using polytropic coefficients, the intercooler by its efficiency. The Ventury effect carburetor model is based on physic properties and the butterfly valve model uses a classical approach. A comparison between the simulation and experimental results is realized in terms of static and dynamic performances in closed loop. Comparisons with actual data obtained on a 210 kW engine shows that the maximum error is less than 5 %.

This paper presents a methodology for a rapid determination of biogas composition using easily detectable physical properties. As biogas is mainly composed of three constituents, it is possible to determine its composition by measuring two physical properties and using specific ternary diagrams. The first part of the work deals with the selection of two physical properties, which are easy and inexpensive to measure, from a group comprising thermal conductivity, viscosity and speed of sound. Then, in the second part, a model to express these properties in terms of ternary composition is presented. It is demonstrated that the composition of a ternary gas mixture can be determined with good precision using the above. The model is applied to specific situations such as the online determination of the lower heating value of biogas without any complicated apparatus like calorimeters or batch techniques (gas chromatographs).

Experiments were conducted on a single cylinder SI engine fuelled by natural gas. Equivalence ratios varying from 0.7 to 1.0 were used and the spark timing was changed from no knock to high knock conditions. Pressure crank angle data from 160 consecutive cycles was analysed. It was found that coefficient of variation of peak pressure (COVPP) and standard deviation of the angle of occurrence of peak pressure (SDAPP) can be used to set the engine for knock free operation. These parameters show a sudden rise from a minimum value that they attain near a spark timing where knock sets in. When the average knock intensity is low, there are two groups of cycles. The first comprises of non-knocking to slightly knocking ones. The other contains cycles with relatively high knock intensity. The sudden emergence of two groups is responsible for the observed trends of SDAPP. At high overall knock intensities the first group is absent.

Experiments were conducted on a single cylinder, natural gas fuelled spark ignition engine. Air fuel ratio was varied from about stoichiometric to the lean limit at two different throttle positions with optimum spark timing. Subsequently the engine was tested at constant throttle and equivalence ratio with variable spark timing. COV (coefficient of variation) of IMEP (indicated mean effective pressure) and peak pressure increase with a reduction in equivalence ratio. When the engine starts to misfire there is a drastic increase in the COV of IMEP. Spark timing has a smaller effect on COV of IMEP than on COV of peak pressure. When the spark timing is advanced, COV of peak pressure attains a minimum value just before knock sets in. Prior cycle effects were seen when there was misfire. Spark timing had little influence on the frequency distribution of IMEPs of cycles, which was generally symmetrical about the mean.

Dual fuel engines can use a wide variety of gaseous fuels efficiently while emitting lesser smoke and particulate than their diesel counterparts. In these engines, a primary gaseous fuel, like biogas, producer gas, LPG etc. supplies the major share of the input energy. The aim of this paper is to characterize the combustion process in a dual fuel engine and to develop a model using a combination simple law of Wiebe. The entire combustion process was divided into 3 stages as follows: the premixed combustion of diesel fuel, the premixed combustion of gaseous fuel and the diffusion combustion. The developed model can be used with good agreement to predict the rate of heat release in a dual fuel engine running at constant load and with variable diesel substitution. A fairly good agreement was observed between the simulation and the experimental results (error smaller than 2%).

A realistic simulation of engine thermal transient behavior requires a coupling between a combustion model and a thermal model of the engine cooling system. This paper describes a procedure used to realize such a simulation. We will develop reasons that lead us towards the choice of Hohenberg's correlation as an engine heat transfer model. A thermal transient simulation of air blown into the car cabin has been computed on a NEDC driving cycle. An experimental study in a wind tunnel has been carried out to validate the heater core heating power and air temperature simulations.

Natural gas composition depends on when and where it is recovered. Variations of composition affect the performance of combustion systems and the accuracy of delivered energy in fiscal gas metering. This paper presents a methodology to determine combustion properties of natural gases (higher heating value, Wobbe index and the stoichiometric air-fuel ratio). A pseudo-gas formulation is used to determine a composition of the most influent constituents of the natural gas. The pseudo-composition is then determined by solving a nonlinear system of equations using thermal conductivity at three levels of temperature and the carbon dioxide concentration. The tested natural gases are chosen to represent typical European gases as well as to account for large variations of individual components. The error on the combustion properties is less than 0.5% for the most of the examined gases and below 1% for gases with high carbon dioxide fractions.

High frequency pressure oscillations are generated under knocking conditions within the combustion chamber of Spark Ignition engines. Although acoustic-oscillation model can give the natural frequencies of these oscillations, very few mathematical models are today available, in scientific literature, to describe the oscillation deadening effect. An analytical formulation of the deadening has been highlighted. Analytical solution has been established for future ECU implementation. Coupling this new concept and an existing high-frequency model, an achieved model of the knocking pressure high frequencies is compared to experimental data. Good behavior is obtained on a natural gas fuelled spark ignition engine.

An extension of a thermodynamic methodology of TDC determination in IC engines is presented. The effect of an error on the TDC position coupled with an error on the compression ratio is analyzed in the temperature-entropy diagram. When the TDC position and the compression ratio are well calibrated, compression and expansion strokes under motoring conditions are symmetrical with respect to the peak temperature in the (T,S) diagram. Moreover, in case of an error on the TDC position, a loop appears, which has no thermodynamic significance. In the same way, in case of a compression ratio error the (T,S) diagram leans. Hence, an easy methodology has been conceived to obtain the right position of TDC and eventually to correct the compression ratio. This methodology is applied on motoring measurements to assess its performance.

A thermodynamic methodology of TDC determination in IC engines based on a motoring pressure-time diagram is presented. This method consists in entropy calculation and temperature-entropy diagram analysis. When the TDC position is well calibrated, compression and expansion strokes under motoring conditions are symmetrical with respect to the peak temperature in the (T,S) diagram. Moreover, in case of error on the TDC position, a loop appears, which has no thermodynamic significance. Hence, an easy methodology has been conceived to obtain the actual position of TDC. This methodology is applied to motoring measurements in order to present its performance, which are compared to usual methods.

Based on a thermodynamic approach, an analysis of a dual fuel combustion, in this particular case Syngas-Diesel, in a CI engine is presented. The influence of fuel substitution on combustion characteristics and engine performances are highlighted. Ignition delay (ID) and combustion models were developed to compute combustion characteristics and exhaust gas emissions. The paper focuses on three combustion stages, each described by a Wiebe law. The developed model ascertains experimental values of the Rate Of Heat Released (ROHR) at different loads and at various substitution rates of diesel fuel. Moreover, an Arrhenius equation law is used to predict NOx emissions. Good agreement with experimental data has been achieved between predicted and experimental data.