A Comparison of Different Low Temperature Combustion Strategies in a Small Single Cylinder Diesel Engine under Low Load Conditions 2017-01-2363

Advanced low temperature combustion (LTC) modes are most promising to reduce green house gas emissions owing to fuel economy benefits apart from simultaneously reducing oxides of nitrogen (NOx) and particulate matter (PM) emissions from diesel engines. Various LTC strategies have been proposed so far and each of these LTC strategies have their own advantages and limitations interms of precise ignition control, achievable load range and higher unburned emissions. In the present work, a small single cylinder diesel engine is initially operated under conventional combustion mode at rated speed, varying load conditions to establish the base line reference data. Then, the engine is modified to operate under different LTC strategies including Homogenous Charge Compression Ignition (HCCI), Premixed Charge Compression Ignition (PCCI) and Reactivity Controlled Compression Ignition (RCCI). The modifications done in the existing engine include a newly designed cylinder head to accommodate a high pressure, fully flexible electronically controlled direct diesel fuel injection system, a low pressure gasoline port fuel injection system, an intake air pre heater and a fuel vaporizer for external mixture preparation. Using a National Instruments (NI) controller, the engine operating parameters interms of direct injected diesel fuel timings, injection pressures, port injected gasoline fuel timings, intake air temperatures, fuel vaporizer temperatures and gasoline to diesel fuel ratio depending upon the type of LTC modes are optimized so as to achieve maximum brake thermal efficiencies. All the three LTC strategies with optimized operating parameters are compared among themselves and also with that of conventional combustion mode at a lower load, rated speed condition. The obtained results show that among all other LTC strategies, RCCI exhibit 8% higher brake thermal efficiency along with near zero NOx and smoke emissions and a lower pressure rise rate.