Experimental Analysis of Hydrogen-Fueled Homogeneous Charge Compression Ignition (HCCI) Engine

Abstract

Hydrogen is a suitable alternate fuel as it can be produced from renewable sources, and also it does not emit carbon monoxide, hydrocarbons, particulates, and carbon dioxide (CO2). The homogeneous charge compression ignition (HCCI) mode is a relatively new engine combustion concept wherein a lean premixed air-fuel mixture is admitted and ignition occurs at multiple points throughout the combustion chamber by compression. The main merits of HCCI are extremely low levels of nitric oxide (NO) and smoke emissions with the potential to develop high thermal efficiency. In this work, experiments were performed on a stationary engine in three different modes of operation, namely, hydrogen-fueled HCCI (HHCCI), hydrogen diesel HCCI (HDHCCI), and neat diesel compression ignition (CI). In the HHCCI mode, thermal efficiency was better than the conventional diesel mode, and emission of NO was very low. The charge temperature had to be held at the lowest level to avoid misfire as this resulted in the best combustion phasing and thermal efficiency. When very early in-cylinder injection of diesel was also employed along with hydrogen diesel HCCI, i.e., HDHCCI mode, intake charge heating was not needed as diesel aided the ignition process. Operation in the neat diesel HCCI mode led to advanced combustion and low thermal efficiency. However, the additional use of hydrogen led to high thermal efficiencies because of proper combustion phasing (combustion occurring close to top dead center). The operating range in the HDHCCI mode was 2–4 bar of brake mean effective pressure (BMEP). Induction of hydrogen also lowered the concentration of NO, smoke, carbon monoxide (CO), and hydrocarbon (HC) emissions as compared to the diesel-based HCCI mode. On the whole, the HHCCI mode is promising in terms of thermal efficiency and low emissions. The HDHCCI operation with common rail injection enables proper combustion phasing and has potential for high thermal efficiency with low emissions. The results indicate that the engine can be operated in the CI mode at low outputs and switch over to HCCI operation with neat hydrogen along with charge heating in the low BMEP range (0.5–2.2 bar). Beyond this output, operation can be in the hydrogen diesel HCCI mode which is viable without heating the intake charge till a BMEP of 4 bar. At higher BMEPs, the engine can only be operated in the neat diesel CI mode.