Hydrogen–Diesel Dual-Fuel Direct Injection in a Compression Ignition Engine

Abstract

This study investigates the performance and emission characteristics of a hydrogen–diesel dual-fuel direct injection (H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>DDI) strategy in a compression ignition engine using AVL FIRE computational fluid dynamics (CFD) simulations. A modified Hyundai D4EA engine model was utilized to evaluate the effects of four hydrogen blending ratios (0%, 20%, 50%, and 80% by energy content) and a range of hydrogen start-of-injection (SOI) timings from 0° to 200° before top dead center (BTDC). The simulation results show that increasing the hydrogen blending ratio significantly improves engine performance when appropriate injection timing is applied. At 80% hydrogen and an SOI of 60° BTDC, the indicated mean effective pressure (IMEP) reached 0.80 MPa, representing a 45.5% improvement compared to 0.55 MPa at 0° BTDC. Similarly, the indicated thermal efficiency (ITE) peaked at 48%, a 39.1% increase from 34.5% at late injection. However, advanced injection beyond 100° BTDC led to a slight drop in performance due to heat losses and premature combustion. Emission analysis revealed that NOₓ emissions peaked at 15.5 g/kWh for 80% hydrogen injected at 80° BTDC, marking a 210% rise from the baseline of 5 g/kWh at 0° BTDC. Earlier injection timings (≥120° BTDC) helped reduce NOₓ levels to 10.5 g/kWh, demonstrating a 32.3% reduction from the peak value. In contrast, lower hydrogen blends such as 20% showed minimal impact on both performance and emissions. These findings highlight the critical importance of optimizing both hydrogen concentration and injection timing to achieve high efficiency while controlling NOₓ emissions in H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>DDI engines.