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A detailed assessment of the various models proposed to simulate the scavenging process in two stroke cycle engines has been made by comparing the charging efficiency and fresh charge fraction in the exhaust gas predicted by the various models. The effect of delivery ratio on the charging efficiency has been studied in detail using different models. It is recommended that a simple two phase model consisting of 50 percent perfect displacement and 50 percent perfect mixing may be used as a satisfactory approximation of the scavenging process. The effect of charge stratification in improving the fuel economy of two-stroke engines has been examined and an analytical preidction of the effect of charge stratification on reduction in fuel loss has been presented.

Based on a multi-zone spray-mixing approach, an air-fuel mixing and combustion model for a Direct Injection Diesel engine is presented. The predictions from the model show very good agreement with the experimental data for various engines under a wide range of operating conditions. Major physical processes are modeled and validated independently. The atomisation process is based on Binary Drop Division concept. Fuel droplets are considered randomly distributed in the spray. A spherico-symmetrical transient drop evaporation model is used for evaporation calculation. A 3-dimensional spray-swirl interaction is modeled on centreline velocity vector/continuum approach. Turbulent mixing is characterised considering all possible available energy sources in DI diesel engines.

The influence of charge non-homogeneity on the cycle-by-cycle variations in combustion for a SI engine was studied experimentally and analyzed theoretically. Charge non-homogeneity was determined from the exhaust gas composition. Cycle-by-cycle variations in the maximum combustion pressure and the angle of maximum pressure were determined by using a real time data acquisition system. A linear relationship between charge non-homogeneity and the cyclic variations in maximum pressure was found. Computed results showed that cyclic variations in maximum combustion pressure increase with increase in charge non-homogeneity at a given mixture strength. For the same charge non-homogeneity, cyclic variations also increase with leaning of the mixture and with increase in the duration of initial phase of combustion.

Cylinder pressure change caused by preliminary introduction of fuel in a CI engine, including introduction during the intake stroke, is measured in both a prechamber and an open chamber engine. Values of ΔP and ΔUF obtained are presented for variation of engine operating conditions such as engine speed, intake temperature, intake pressure, and compression ratio. Cetane number, voltaility, and quantity of preliminary fuel were also varied. The results show that if the preliminary fuel is injected sufficiently early it passes through two distinct stages of exothermic reactions separated by an induction period during which the reaction rate is low. The preliminary fuel, by virtue of its longer residence time, completes the required sequence of physical and chemical transformations during the compression stroke.

An investigation into effects of multiple fuel introduction on isfc, rate-of-pressure rise, ignition delay, and smoothness of P-T diagram was conducted. Work, including pilot and manifold injection and the Vigom process, was conducted in a prechamber, an open chamber, and a Ricardo Comet chamber, all mounted on a CFR crankcase. Results show marked smoothening of the P-T diagram, with slight loss in fuel economy, particularly in the open chamber, and decrease in ignition delay for both high and low cetane fuels, especially at lower engine speeds. Data show that the quantity of preliminary fuel required for best performance changes considerably with cetane number of the fuel and with combustion chamber.