The Influence of Hydrogen Direct Injection on the Combustion Characteristics of a Compression Ignition Engine

Hydrogen, as a clean and sustainable energy carrier, has been widely considered by many researchers in internal combustion engine (ICE) application as a primary fuel or in combination with other conventional fuels such as diesel and gasoline. To date, several studies have focused on investigation on premixed PFI (port fuel injection) hydrogen internal combustion engine (H2ICE) which suffers from lower power output and combustion efficiency, due to low density of hydrogen. In this study, computational fluid dynamics (CFD) using Converge software is utilized to evaluate the combustion performance of a hydrogen-diesel dual fuel compression ignition (CI) engine considering direct injection strategy of hydrogen which enhances the volumetric efficiency of the engine cycle. The combustion characteristics of the engine for five different hydrogen energy shares (HES) from 10 % to 50 % and three different hydrogen injection timings have been investigated. The results revealed that the addition of hydrogen increases the acceleration of heat release rate (HRR) and the combustion peak pressure (P-max) by 43 % for 50 % HES. Since hydrogen addition accelerates the combustion speed, the combustion duration is reduced by 90 %, leading to a nearly constant volume combustion, therefore the thermal efficiency of the hydrogen-diesel CI engine is comparable to or higher than diesel-only fueled mode. Having increased HES resulted in lower carbon monoxide (CO), carbon dioxide (CO2) and soot, however, hydrogen deteriorated NOx concentration as a matter of higher combustion average temperature.