Experimental Investigation of the Near-Zero Emission Turbocharged Direct-Injection Hydrogen Engine

Abstract

Many countries have committed to achieving peak carbon dioxide emissions in recent decades, and it is necessary to implement low-carbon or carbon-free energy. Hydrogen, as clean and renewable energy, is regarded as a promising fuel applied to the internal combustion engine. Nitrogen oxidize (NOx) is the only emission of the hydrogen engine, since other emissions such as HC and CO caused by the consumption of the engine oil can be neglected. The direct-injection (DI) hydrogen engine has been demonstrated to offer large power without the risk of abnormal combustion. In this study, a 2.0L turbocharged direct-injection engine is used to achieve higher power and thermal efficiency with nearly zero original emission (reaching approximately zero NOx emission without any post-treatment equipment). The target of the NOx emission is set below 20 ppm according to the emission standards. The effect of the coefficient of excess air (λ), the timing of the start of injection (SOI), and injection pressure on the NOx emission are investigated in detail. The mixing duration and the intake pressure rise with the increase of the engine speed. Therefore, a leaner combustion (λ=3.29@ 3000 rpm) compared to the λ=2.62@ 2000 rpm is required to reduce the combustion temperature to achieve near-zero emission. The utilization of the turbocharger and improvement injection pressure increase the `power and the efficiency simultaneously. The maximum brake mean effective pressure (BMEP) can reach 13.3 bar@3000 rpm, and the maximum brake thermal efficiency (BTE) arrives at 40.4% @2000 rpm with near-zero NOx emission. Various techniques such as turbocharger, exhaust gas recirculation, and increased compression ratios are also compared to qualify the trade-off relationships among the power, the efficiency, and the emission of the direct-injection hydrogen engine. These conclusions can be used to broaden the working boundary and optimize the fuel economy of the near-zero NOx emission turbocharged direct-injection hydrogen engines.

Keywords: Direct-injection hydrogen engine, Lean combustion, NOx control, Nearly-zero emission