The potential in efficiency improvement of in-cylinder thermochemical fuel reforming in natural gas engines

Abstract

With decarbonization becoming the primary focus of the automotive industry, high-efficiency and low-emission engine technologies have garnered increasing attention. Among the advanced technologies, fuel reforming is a promising way to reduce emissions and increase efficiency with hydrogen generated onboard. This paper focuses on the potential of improving efficiency using in-cylinder thermochemical fuel reforming combustion in natural gas engines. The experimental results revealed that combustion in the reforming cylinder inevitably deteriorates, and hydrogen generated by fuel reforming could not counteract the slower combustion due to fuel enrichment. However, the presence of hydrogen in the nonreforming cylinder significantly increased the flame propagation speed, hence improving combustion efficiency. After a series of variable-parameter tests, it was found that the appropriate reforming equivalence ratio was 1.15 at low load and ∼1.2–1.3 at medium to high loads, with efficiency increased up to 4–5% and 8–12%, respectively. Dual-fuel reforming combustion experiments were conducted using a rapid compression machine and a single-cylinder engine to further explore the fuel reforming combustion. The results suggested that, at medium load, the combustion instability in the reforming cylinder can be solved by adopting two-stage combustion at an equivalence ratio of 1.3, and the indicated thermal efficiency could reach 43%. Based on the research results, a remarkable potential improvement in efficiency can be achieved if reforming combustion is successfully implemented. Dual-fuel reforming has the most potential to achieve an even higher engine efficiency, and its practical issues such as transient engine control and soot formation deserve further investigation.