Conceptual Approach on Feasible Hydrogen Contents for Retrofit of CNG to HCNG under Heavy-Duty Spark Ignition Engine at Low-to-Middle Speed Ranges

Abstract

Hydrogen-based engines are progressively becoming more important with the increasing utilization of hydrogen and layouts (e.g., onboard reforming systems) in internal combustion engines. To investigate the possibility of HICE (hydrogen fueled internal combustion engine), such as an engine with an onboard reforming system, which is introduced as recent technologies, various operating areas and parameters should be considered to obtain feasible hydrogen contents itself. In this study, a virtual hydrogen-added compressed natural gas (HCNG) model is built from a modified 11-L CNG (Compressed Natural Gas) engine, and a response surface model is derived through a parametric study via the Latin hypercube sampling method. Based on the results, performance and emission trends relative to hydrogen in the HCNG engine system are suggested. The operating conditions are 1000, 1300, and 1500 rpm under full load. For the Latin hypercube sampling method, the dominant variables include spark timing, excess air ratio (i.e., lambda(CH4+H2)), and H(2)addition. Under target operating conditions of 1000, 1300, and 1500 rpm, the addition of 6-10% hydrogen enables the virtual HCNG engine to reach similar levels of torque and BSFC (brake specific fuel consumption) compared to same lambda condition of lambda(CH4). For the relatively low 1000 rpm speed under conditions similar to those of the base engine, NOx formation is greater than base engine condition, while a similar NOx level can be maintained under the middle speed range (1300 and 1500 rpm) despite hydrogen addition. Upon addition of 6-10% hydrogen under the middle speed operation range, the target engine achieves performance and emission similar to those of the base engine.