Numerical and Experimental Analysis of Dual Fuel Hydrogen/Diesel Combustion at Varying Engine Speed on a Single Cylinder Engine

Reduction of CO2 emissions from transportation is mandatory to limit global warming. New Energy Vehicles (NEV) need to be used widely in order to reach this goal. NEV include Battery Electric Vehicles (BEV), Hybrid Electric Vehicles (HEV), Plug-in Hybrid Electric Vehicles (PHEV) and Fuel Cell Electric Vehicles (FCEV). From a Life Cycle Analysis point of view, considering the CO2 emissions produced by battery manufacturing and during vehicle use, the most promising technology is the PHEV operating on green fuels. However, the internal combustion engine remains a source of gaseous pollution in urban areas. The combustion process has to be further improved to comply with latest and most stringent exhaust emission standards. One way to achieve this objective is the use of eco-friendly fuels like hydrogen to reduce engine-out emissions (NOx, soot and CO2) in PHEV system. The aim of the present work is to analyze the dual-fuel (DF) technology, in which a small amount of diesel fuel is injected directly in the cylinder to ignite port fuel injected hydrogen. The DF concept represents an alternative solution to reduce engine emissions by using hydrogen. Besides, this possible technology can be applied to current diesel engines without significant change of engine design. In this study, dual fuel combustion process has been investigated numerically and experimentally in a single cylinder research engine. Two engine speeds have been investigated (1500 and 2000 rpm) at fixed BMEP of 5 bar for both engine speeds. For each engine speed two operating points have tested with and without EGR (Exhaust Gas Recirculation). The hydrogen has been injected in the intake manifold in front of the tumble intake port inlet and a small amount of diesel fuel has been introduced directly in the cylinder through two injections strategy: one pilot injection occurring Before Top Dead Center (BTDC) and one main occurring around the Top Dead Center (TDC). The dual-fuel combustion model in GT-SUITE has been used first to calibrate the combustion model by using the Three Pressure Analysis (TPA) model. This step allows the calibration of the combustion model to predict in-cylinder combustion processes. Simulations have been performed at varying mass distribution of injected diesel fuel during pilot and main injections at fixed start of pilot injection (SOIp). For both engine speeds it was found that the model predicts well the in-cylinder pressure traces, the ignition delays, the heat release rates and NOx emissions. The simulated results at varying mass distribution of injected diesel fuel between the pilot injection and the main injection, have shown that the distribution has no effect on the ignition delay times. This distribution mainly controls the combustion duration and NOx emissions. Indeed, when the amount of diesel pilot injection is increased the NOx emissions are increased by around two for all engine operations. As expected, when a small amount of EGR is used the NOx emissions are lower compared to the operations without EGR. This first step of parametric analysis of DF combustion shows that further investigations are required into the dual-fuel (H2 /diesel) combustion to optimize engine performances and emissions.