Effect of Split Injection on Combustion and Performance of a Biogas-Diesel Fuelled PPCCI Engine 2015-24-2453
In this experimental work the effect of double injection of diesel in a biogas-diesel partially premixed charge compression ignition (BDPPCCI) engine was studied. Biogas was inducted along with air while diesel was injected through a common rail system using an open electronic control unit. Experiments were done at a fixed brake mean effective pressure of 2 bar and an intake charge temperature of 40°C. The effect of start of injection (SOI) of first and second injection pulses and also the biogas energy share (BGES) were evaluated. Experiments were also done in the BDPPCCI mode with diesel being injected in a single pulse and in the biogas-diesel dual fuel (BDDF) mode for comparison. The thermal efficiency in the BDPPCCI mode was better with double injection of diesel as compared to single pulse injection due to better combustion phasing. Improved charge homogeneity and reduced wall wetting of diesel lowered the smoke emission levels with split injection. Nitric oxide (NO) and hydrocarbon (HC) emissions were similar between split and single injection in the BDPPCCI mode. Further the BDPPCCI mode was significantly better than the BDDF in terms of NO and HC emissions. However, at high BGES the thermal efficiency with the BDPPCCI mode with single pulse injection was better than the BDDF mode. With split injection this threshold energy share could be lowered and thus the operating range of energy ratios was widened in the BDPPCCI mode.