Experimental Investigations to Extend the Load Range of Premixed Charge Compression Ignited Light Duty Diesel Engine through Fuel Modifications

Premixed Charge Compression Ignition (PCCI) is one of the most promising low temperature combustion (LTC) strategies to achieve near zero oxides of nitrogen (NO_x) and particulate matter (PM) emissions along with higher thermal efficiency. One of the major problems in diesel PCCI is a narrow operating load range because of very early ignition and knocking combustion at higher loads owing to higher reactivity of diesel fuel. Further, low volatile diesel resist vaporization, resulting in fuel spray wall wetting and higher unburned emissions in PCCI. Thus, high reactivity and low volatility of diesel fuel make it not suitable for PCCI combustion. The present work attempts to address these limitations, by blending diesel with high volatile and low reactive fuels, viz. gasoline and butanol at 10% and 20% blend levels by volume. A production light duty air cooled diesel engine most widely used in agricultural water pumping applications is modified to run in PCCI mode by replacing an existing mechanical fuel injection system with a flexible common rail injection system. The test engine is initially run in diesel PCCI mode to establish the baseline reference data. The direct injected (DI) diesel fuel timings and exhaust gas recirculation (EGR) concentration are optimized at each load conditions to achieve maximum brake thermal efficiency. The results obtained show that the engine could be operated only upto 40% of rated load in diesel PCCI mode beyond which it knocks severely. The engine is then operated with diesel-gasoline and diesel-butanol blends at 10% and 20% blend levels at similar operating conditions. Among the investigated fuel blends, 20% butanol with 80% diesel (DB20) perform better in terms of achievable load range and lower carbon monoxide emissions. Optimization of DI timings and EGR concentration with DB20 helps to extend the load range upto 60% of rated load. The NO_x and smoke emissions are significantly lower in PCCI with all the tested fuels.