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Item Pre combustion energy release and its effect on flame propagation and exhaust emissions in a spark ignition engine(1977) Samaga, B.S.; Murthy, B.S.The extents of pre combustion reaction and cumulative pre combustion energy release have been computed for various operating conditions in a single cylinder variable compression ratio research engine. Exhaust emission levels of CO and HC are measured by gas chromatography. The mean turbulent flame propagation velocity is estimated from a thermodynamic analysis of the engine cylinder pressure trace. The effect of pre combustion energy release on the flame velocity and the exhaust emissions of CO and HC has been discussed. It is found that the pre combustion energy release may account for as much as 20% of the heat in the fuel in the case of reactive fuels of relatively low octane numbers. In general, increased pre combustion reactivity is found to decrease CO and HC emission levels. However, its effect on the mean engine flame velocity does not appear to be pronounced.The extents of pre-combustion reaction and cumulative pre-combustion energy release have been computed for various operating conditions in a single cylinder variable compression ratio research engine. Exhaust emission levels of CO and HC are measured by gas chromatography. The mean turbulent flame propagation velocity is estimated from a thermodynamic analysis of the engine cylinder pressure trace. The effect of pre-combustion energy release on the flame velocity and the exhaust emissions of CO and HC has been discussed. It is found that the pre-combustion energy release may account for as much as 20% of the heat in the fuel in the case of reactive fuels of relatively low octane numbers. In general, increased pre-combustion reactivity is found to decrease CO and HC emission levels. However, its effect on the mean engine flame velocity does not appear to be pronounced.Item Exhaust emission characteristics correlated to a chemically equilibrating gaseous system in an SI engine(1976) Samaga, B.S.The chemical reactions leading to the destruction of NO and CO in the engine combustion gases are temperature dependent and it has been observed that they change over from 'shifting' equilibrium to 'frozen' equilibrium as the temperature drops during the expansion phase. Application of reaction rate theories to the prediction of exhaust emissions is complex and can at best be an approximation owing to uncertainties of the engine combustion reaction mechanism, the assumed rate constants and the estimated combustion temperatures. An attempt was made to correlate the computed equilibrium concentrations during the expansion phase to the measured emission levels of NO and CO to estimate the temperatures at which nonequilibrium effects become apparent. Comparison of the measured emission levels from a single cylinder spark ignition engine with the computed equilibrium concentrations for several engine operating conditions has shown that the concentration of NO freezes near its peak equilibrium value, whereas the destruction of CO continues during the subsequent expansion phase until the temperature has dropped to an effective 'frozen equilibrium temperature' at which the computed equilibrium CO corresponds to the measured level in the exhaust. This temperature is dependent on the time rate of expansion and was determined to be 1250 K at 600 rpm and 1300 K at 900 rpm for the steady state operating conditions considered in the present series of tests.An attempt has been made to correlate the computed equilibrium concentrations during the expansion phase to the measured emission levels of NO and CO to estimate the temperatures at which nonequilibrium effects become apparent. Comparison of the measured emission levels from a single cylinder spark ignition engine with the computed equilibrium concentrations for several engine operating conditions has shown that the concentration of NO freezes near its peak equilibrium value, whereas the destruction of CO continues during the subsequent expansion phase until the temperature has fallen down to an effective 'frozen-equilibrium temperature' at which the computed equilibrium CO corresponds to the measured level in the exhaust.Item On the problem of predicting burning rates in a spark ignition engine(1975) Samaga, B.S.; Murthy, B.S.In this paper, formulation of a mathematical model for flame propagation in a spark ignited reciprocating engine has been described. As against the common practice of assuming a laminar flame propagation model with a suitable multiplying factor for turbulence effects, a more logical approach has been adopted bringing in the concept of an engine Reynolds parameter as the criterion to determine the combustion acceleration due to turbulence. The laminar burning velocity is calculated from Semenov's thermal model for the instantaneous unburned gas condition during combustion and is augmented for engine gas turbulence through an empirical function of the engine Reynolds parameter assuming wrinkled flame model. The turbulent flame velocity thus obtained is then corrected for flame transportation due to the expansion of the burning gases. The empirical constants in the formula have been evaluated in correlation to results of extensive experimentation on a single cylinder variable compression ratio research engine.Item Investigation of a turbulent flame propagation model for application for combustion prediction in the S.I. engine(1976) Samaga, B.S.; Murthy, B.S.This paper is a follow-up of the authors' earlier paper(1)* in which the development and evaluation of a mathematical model for turbulent flame propagation in the S.I. Engine had been described. The present paper gives a report of further studies regarding the general applicability of this model for S.I. engine combustion prediction. A simplified scheme has also been suggested to predict the pollutant emission by a correlation of the computed equilibrium mole fractions to the measured emission levels of 'CO' and 'NOx' in the exhaust. A wide variety of operating conditions has been considered and the model is applied in a simulation program to compute the combustion and exhaust emission characteristics for each operating condition. The predicted results, in general, are in conformity with the experimentally measured results reported in literature. Copyright � 1976 Society of Automotive Engineers, Inc. All rights reserved.