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During the development of dual intake port for a lean burn engine, the conventional method of port characterization, using flow coefficients, was found to be inadequate. A suitable strategy was devised which uses the results from steady state flow bench to compute the total flow through the port at an indicative engine speed and for a particular valve lift behavior. A proper basis for comparison of the baseline single intake port with the developed dual intake port was thus arrived at.

Engine maps consisting of three-dimensional contour plots of engine performance parameters such as bsfc in the engine speed - bmep plane give a large amount of information in a very concise manner. Such maps can be drawn for many more parameters of interest if a high speed data acquisition system, such as E-DACS (Engine Data Acquisition and Control System) which was developed in-house, is used to obtain the transient data of combustion chamber pressure. New maps of: pmax, (dp/dθ)max, etc. from the pressure-crank angle data; isfc, imep, pumping losses, etc. from the pressure-volume data; ignition delay, burn angle, maximum rate of burning, maximum burnt gas temperature, etc. after conducting heat release analysis using the pressure-crank angle data, can be generated. Such an enlarged view offered by these new sets of engine maps will definitely prove useful to engineers, giving them newer insights.

Heat release analysis brings out the various phenomena that cause the development of the combustion chamber pressure. A three-zone heat release model computes the rate of heat release and other properties of all the three zones (representing vaporized fuel, unburnt and burnt gas zones) from measured pressure-crank angle data obtained from an instrumented engine. It is a useful diagnostic tool giving a great deal of information about an existing engine. Heat release analyses for five different operating conditions have been conducted for a DI diesel engine. Also, ignition delay, wall heat losses and mass, volume and temperature in each of the three zones have been computed. It is found that the overall quality of the computed heat release rates are strongly dependent on the accuracy of the measured pressure data. The model can be integrated to a high speed data acquisition system for concurrent analysis of the heat release patterns.

Dual spark plugs are occasionally employed on certain modem S.I. engines operating with very lean fuel-air mixtures, or with larger proportion of EGR, or on engines operating in other conditions which are difficult to ignite. Different researchers have advanced different reasons for gains due to dual spark plugs; namely, shorter flame travel distance, change in flame speeds and shapes, etc. According to the hypothesis proposed by the present author, the exact cause of the gains due the dual plug system is different from that put forth by the other researchers. The hypothesis states that, in adverse engine operating conditions when the success rate of spark ignition is poor, the presence of two spark plugs increases the probability of generation of the self-sustaining flame kernel thereby reducing the probability of misfires. The hypothesis is proved by conducting a brief parametric study using a validated mathematical model.

Development of mathematical models for internal combustion engines has received the attention of several researchers in the last two decades. The goal is to generate mathematical models which can be used to design future engines and improve the present ones. However, a mathematical model can be used as an engine design tool only if it has been proved to be reliable by way of conducting an extensive validation exercise. A general philosophy has been outlined which will help one select the system configurations to generate experimental data for a validation exercise. The related questions on interpretation of measured data have also been examined. Variation of model constants to generate model results for different system configurations has also been considered. The above ideas have been put forth in the form of ten important statements along with their explanations and illustrations given in the context of I.C. engines.

A new engine concept has been proposed wherein a very lean premixed fuel-air mixture is inducted and compressed to a very high compression ratio with fuel of such an octane quality that the autoignition occurs throughout the charge simultaneously at or slightly after TDC (the homogenous charge simultaneous autoignition engine or HCSA engine). The HCSA engine promises very high efficiency due to high compression ratio and high air-fuel ratio and less pollutants due to high air-fuel ratio. A detailed and tested two-dimensional mathematical model with a tested sub-model for the autoignition process was used to prove that the HCSA engine will operate efficiently in a wide range of engine speed and load. The indicated thermal efficiency had its average value around 40%.

A zero-dimensional (or, quasi-dimensional) model for combustion in S.I. engines has been developed using conservation equations for mass and energy, thermodynamic state equations and correlations for mass burning rate and wall heat transfer. The model was applied to a single cylinder, four-stroke gasoline engine. The computed pressure crank angle results were compared with the measured pressure histories obtained for nine engine operating conditions representing various engine speeds, air-fuel ratios, and loads. The extensive comparison study, which hitherto had not been conducted to validate any zero-dimensional model, ended with surprising success in view of the fact that the zero-dimensional model is very simple and an engine is a very complex system. Satisfactory comparisons were obtained simultaneously for all the operating conditions with only one set of model constants. The spark timings used in the computations were same as the actual ones.

Two versions of a zero-dimensional heat release model have been utilised to compute the mass of the gases in the burned zone in a two-stroke gasoline engine for which measured pressure -crank angle data were available. The two sets of the mass fraction burned profiles, obtained for 10 different engine operating conditions, showed satisfactory behaviour. The model results contain useful informations about the combustion phenomena occurring in the engine which otherwise are difficult to measure. In addition, the gas exchange parameters were also known from the computed results. Such model results will certainly be an asset to an engine designer. The model, consisting of only algebraic equations, requires very small computer time and thus, can be integrated with a computer based data acquisition system to monitor the mass burning behaviour on a real time basis.