Realizing low NOx emissions on a hydrogen-fuel spark ignition engine at the cold start period through excess air ratios control

In this paper, the effects of excess air ratios (λ) on nitric oxide (NOx) emissions of a hydrogen-fueled spark ignition engine in the cold start period are studied. Cold start characteristics of hydrogen-fueled engine were investigated experimentally. The study was performed under different λ. The experimental results showed that, when λ declined from 1.6 to 0.7, the peak engine speed within the first 6 s increased and in-cylinder pressure in the first cycle raised firstly then decreased slightly while the flame development and propagation periods shortened, and the exhaust temperature at the 6th s raised from 329 K to 355 K. In addition, NOx emissions obviously decreased, whereas hydrocarbon (HC) and carbon monoxide (CO) emissions caused by the evaporated lubricant oil increased by decreasing λ within the first 6 s.