Charge Dilution Strategy to Extend the Stable Combustion Regime of a Homogenous Charge Compression Ignited Engine Operated With Biodiesel 2023-32-0132

The present research explores the application of biodiesel fuel in a stationary agricultural engine operated under the Homogenous charge compression ignition (HCCI) mode. To achieve HCCI combustion, a fuel vaporizer and a high-pressure port fuel injection system are employed to facilitate rapid evaporation of the biodiesel fuel. The low volatility of biodiesel is one of the significant shortcomings, which makes it inevitable to use a fuel vaporizer at 380oC. Consequently, the charge temperature is high enough to promote advanced auto-ignition. Further, the high reactivity of biodiesel favors early auto-ignition of the charge. Besides, biodiesel exhibits a faster burn rate due to its oxygenated nature. The combined effect of advanced auto-ignition and faster burn rate resulted in a steep rise in the in-cylinder pressures, leading to abnormal combustion above 20% load. Diluting the charge reduces reactivity and intake oxygen concentration, facilitating load extension. This study explores two charge diluents: recirculated exhaust gas (EGR) and water vapor induction into the intake manifold. With EGR, the maximum load is 40%, whereas 46% of the rated load could be achieved with water vapor induction. The maximum load could be extended up to 50% with the combined dilution using EGR and water vapor. The charge dilution required with water vapor is less than that of EGR. Additionally, charge dilution with water vapor results in better thermal efficiency, fuel economy, and lower emissions than EGR. Overall, the present study confirms the functionality and feasibility of biodiesel in HCCI engines, demonstrating the applicability of charge dilution to address its significant shortcoming of a narrow stable combustion regime.