The main objective of this computational study is to investigate the optimum injection and spark parameters for the direct injection spark ignition (DISI) Wankel rotary engine using diesel fuel. Currently only port fuel injected gasoline rotary engines are available in the automotive industry. Compared to reciprocating type engines rotary engine is mechanically simple, less vibrate, have higher power to weight ratio and achieve better performance at high rpm. Due to the inherent low fuel efficiency of rotary engine and increasing gas prices, application of the rotary engine in conventional automobiles is decreasing. This project seeks to introduce DISI technology to the rotary engine thus increase the fuel efficiency allowing it to be another efficient power source option for aero and automotive applications.
DISI technology is the latest trend in the automobile manufacturing. This technology helped to combine benefits of both compression ignition (CI) and spark ignition (SI) engines into a single efficient internal combustion process. Multi-fuel capabilities, reduced operating pressures, and reduced compression ratios make this technology applicable for rotary engines. In this study diesel fuel, as opposed to gasoline, is introduced into the rotary engine using DISI technology.
Due to high technological advancements used in DISI engines, it is expensive to experimentally incorporate this technology to a new engine. Accurately designed computational analyses can reduce both time and cost by cutting extra experimental test trials. For this computational fluid dynamics (CFD) study ANSYS FLUENT commercial software was used to integrate the DISI technology into a rotary engine model which was designed in Solidworks and meshed in GAMBIT.
When creating the engine model, many parameters have to be considered. Engine geometry, injectors, and spark plugs were identified as the most important components needed to be investigated when integrating DISI technology into the rotary engine. By using a readily available rotary engine, direct injector, and spark plug, the number of parameters for the optimization process were reduced. The most important parameters were picked to evaluate the optimum single injection and spark locations. Full factorial experimental design was used to estimate the sensitivity of different combinations of parameters. This was followed by a statistical sensitivity study using JMP 800 commercial software to determine the most and least sensitive parameters to analyze for the optimum setup of single injection rotary engine combustion. Contour plots of fuel consumption, CO2 generated, equivalence ratio, average temperatures, and pressures were used to support the results.
The feasibility of multiple injections was also studied by means of their power outputs and fuel efficiencies. Optimum locations, amounts of fuel, number of orifices and orientations of orifices were included when evaluating optimum lead (second) injector. Similar studies were carried out to check the applicability of a third injector. From the results it can be observed that a dual injection setup provided optimum performance from the DISI rotary engine.