A Numerical Study of Injection Strategies for Zero-Carbon Compression Ignition Hydrogen Engines

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This study investigates strategies for igniting hydrogen in compression ignition engines, a process traditionally hindered by hydrogen’s high ignition temperature. In conventional dual-fuel engines, a small diesel pilot is often used to ignite hydrogen, taking advantage of diesel’s lower ignition temperature to initiate combustion. While effective, this approach introduces carbon emissions, limiting the potential for fully zero-emission operation. Recognizing the high efficiency of compression ignition, we investigate an alternative to the dual-fuel diesel pilot approach. Our research focuses on developing and assessing advanced injection strategies to achieve reliable and controllable hydrogen ignition without the need for diesel pilots. Through extensive numerical simulations, we scrutinize the dynamics of hydrogen injection and combustion within a conventional heavy-duty compression ignition engine. Our initial results indicate that a two-stage hydrogen injection strategy, consisting of a pilot injection followed by a main injection, enables stable combustion while maintaining an indicated thermal efficiency of 52.7%. This was achieved by increasing the intake air temperature by 30 K to facilitate hydrogen auto-ignition. However, this elevation in temperature leads to increased NO x emissions with values as high as 34.4 g/kWh of NO x and reduced efficiency. To address this, we introduce an injection strategy involving a pilot injection of hydrogen and a delayed main injection at varying dwell times, successfully igniting hydrogen while minimizing NO x emissions. For the optimized case, NO x emissions were reduced to 17.4 g/kWh. This strategy not only ensures efficient combustion but also significantly reduces environmental impact, marking a pivotal step toward sustainable, hydrogen-powered transportation.

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