Shamit Bakshi

A Gasoline Direct Injection (GDI) engine typically operates on multiple fuel-preparation modes. In general, at higher loads a homogeneous mixture is favoured whereas a stratified mixture is preferred at part and low load conditions. This is usually achieved by altering the injection timing with respect to load and speed. In this paper the effect of injector configuration on the mixing process has been studied systematically. Two different injector configurations are considered, one with a central-hole injection and other with a 6-hole injection. The objective is to investigate the effect of initial fuel distribution inside the engine cylinder on charge preparation at the onset of ignition. This study also aims to explore a better solution for mixing in GDI engines by optimizing the GDI injector for both stratified and homogeneous mode of operations. An engine with a pentroof combustion chamber with centrally mounted injector and upright straight intake port and flat piston is selected. The computation begins from the start of the induction process and continued till the point of ignition. The dynamics of the mixing process is studied by grouping the in-cylinder charge in different bins in terms of the equivalence ratio. The temporal variation of the fraction of the mixture in different bins is studied as a function of time to understand the dynamics of the mixing process. Results from the parametric study indicate the possibility of switching the modes of mixing with respect to the operating conditions.

A gasoline direct injection engine typically operates in multiple fuel preparation modes. In general, at higher loads, a homogeneous mixture is favored, whereas a stratified mixture is preferred at part- and low-load conditions. This is usually achieved by altering the injection parameters and injection strategy with respect to load and speed and through appropriate cylinder and piston geometries. In this article, a new injector concept has been proposed to aid attaining multiple modes in a gasoline direct injection engine. This is achieved by shaping the spray structure to suit the required mixture preparation. Detailed simulations are performed to assess the mixing process in a gasoline direct injection engine using the new injector. The charge preparation at the onset of ignition is studied for different injection modes of the same injector. The results indicate a significant improvement in the mixing process for different modes of operation. © IMechE 2013.

Short-circuiting of the fuel air mixture during scavenging is the main reason for high fuel consumption and hydrocarbon (HC) emissions in two-stroke SI engines. Though direct injection of the fuel after the closure of ports has advantages, it is costly and complex. In this work, in a 2S-SI, single cylinder, automotive engine, LPG (liquefied Petroleum Gas) was injected through the boost port to reduce short-circuiting losses. A fuel injector was located on one of the boost ports and the air alone was fed through the other transfer and boost ports for scavenging. Experiments were done at 25% and 70% throttle openings with different injection timings and optimal spark timing at 3000 rpm. Boost port injection (BPI) of LPG reduced HC emissions at all conditions as compared to LPG-MI (Manifold Injection). Particularly significant reductions were seen at high throttle conditions and rich mixtures. HC reductions with BPI were 19% and 25% as compared to LPG-MI and gasoline-MI respectively. BPI resulted in almost the same efficiency as LPG-MI except at lean mixtures, particularly at high throttle conditions. At 25% throttle the brake thermal efficiency with BPI was similar to LPG-MI. With lean mixtures at 70% throttle conditions lower heat release rates were observed with BPI. NO emissions are higher with BPI as compared to LPG-MI when the mixture was rich due to improved heat release rates. However, the peak value of NO is always lower than gasoline-MI. Copyright © 2013 SAE International.

Conventional two-stroke, spark-ignition engines exhibit poor fuel economy and emit high hydrocarbon (HC) emissions due to short-circuiting of the fuel-air mixture. Literature suggests that the use of LPG in two-stroke engines poses further problems in terms of higher HC emissions. In this work, timed compressed air injection into the transfer ducts with LPG induction through the manifold (AI-LPG-IND) was adopted to reduce short-circuiting losses in a two-stroke spark-ignition engine. The engine was fully instrumented for performance, emission and combustion related measurements. Gaseous LPG injection through one of the boost ports (LPG-BPI) of the engine was also attempted. Experimental results at 25% and 100% throttle were compared with manifold injection of LPG (LPG-MI) and gasoline at the best spark timing. The AI-LPG-IND system resulted in 40% reduction in HC emissions as compared to the LPG-MI system with a simultaneous increase in the power output at 25% throttle. It was also better than the LPG-BPI system in terms of emissions at this condition. However, due to the relatively small quantity of injected air at 100% throttle, the AI-LPG-IND system was similar in performance to the LPG-MI. The LPG-BPI system reduced HC emissions at 100% throttle, but the thermal efficiency was lower than other systems.© 2014 Elsevier Ltd. All rights reserved.

Abstract Improvements in a two-stroke, spark-ignition (2S-SI) engine can be realized by curtailing short-circuiting losses effectively through direct injection of the fuel. Liquefied petroleum gas (LPG) is an alternative transportation fuel that is used in several countries. However, limited information is available on LPG fuelled direct injected engines. Hence, there is a need to study these systems as applied to 2S-SI engines in order to bring out their potential benefits. A manifold injected 2S-SI engine is modified for direct injection of LPG, in gaseous form, from the cylinder head. This engine is evaluated for performance, emission and combustion. Evaluation at various throttle positions and constant speed showed that this system can significantly improve the thermal efficiency and lower the hydrocarbon (HC) emissions. Up to 93% reduction in HC emissions and improved combustion rates are observed compared to the conventional manifold injection system with LPG. CO emissions are higher and peak NO emissions are lower with this system due to the presence of richer in-cylinder trapped mixtures and charge stratification. This system can operate with similar injection timings at different throttle positions which make electronic control simpler. It can work with low injection pressures in the range of 4-5 bars. All these advantages are attractive for commercial viability of this engine.