Exploring the Possibility of Achieving Partially Premixed Charge Compression Ignition Combustion of Biodiesel in Comparison to Ultra Low Sulfur Diesel on a High Compression Ratio Engine

The combustion characteristics of biodiesel operating in the Low Temperature Combustion (LTC) regime, via Partially Premixed Charge Compression Ignition Combustion (PPCI), is relatively unknown. Therefore, this study compares engine performance and emissions of ultra-low sulfur diesel (ULSD) and waste cooking oil biodiesel through an attempted PPCI methodology. The Fuel Injection Timing (FIT) was gradually altered from conventional combustion timing (12.0 degrees for biodiesel and 12.5 degrees for ULSD) to 35.0 degrees before top dead center. Results indicated that the fuel consumed to maintain the required load condition increased gradually for both ULSD and biodiesel due to the start of combustion shifting further into the compression stroke for each injection advancement. Nitrogen oxides (NOx), particulate matter (PM), carbon monoxide, and total hydrocarbons were marginally lower for biodiesel compared to ULSD. There was limited success in reducing both NOx and PM emissions simultaneously by varying the FIT alone for both fuels. The high compression ratio of the engine utilized was a major limiting factor in achieving LTC. Importantly, the Negative Temperature Coefficient (NTC) behavior of biodiesel and its impact on ignition delay was successfully captured. The operating conditions used in this study are closer to a production engine as compared to shock tube and constant volume combustion systems typically used to validate chemical kinetic (CK) models. Moreover, data surrounding NTC and its influence on ignition delay with biodiesel in CI engines is limited in the literature. Thus, the results presented provide valuable data that could be utilized to help validate CK models investigating the behavior of biodiesel fuels.