Hydrocarbon impact on NO x survivability during diesel low-temperature combustion cycles

Abstract

Abstract

Low-temperature combustion (LTC) cycles are inherently inclined to produce higher amounts of combustibles because the burning of a homogeneous cylinder charge that is lean and/or exhaust gas diluted is closer to the non-combustion regions (flame-out limits). However, the impact of the hydrocarbons produced during the LTC cycles on the attainment of ultra-low levels of nitrogen oxides (NO _x ) is less understood, and it is unclear whether the hydrocarbon species are a precursor to the ultra-low NO _x and also contribute in part to the NO _x reduction. Therefore, the impact of the hydrocarbon emissions on the NO _x emission of the LTC cycles has been empirically investigated on a number of common-rail diesel engine platforms of high compression ratios. The empirical studies have been conducted under independently controlled exhaust gas recirculation, intake boost, and exhaust back pressure. The survivability of NO _x under the compression and combustion processes has been presented in the context of the quasi-steady exhaust NO _x and the effect of the hydrocarbons on the NO _x survivability has been quantified. The chemical impact of the hydrocarbon species on the NO _x emission under LTC cycles has been examined with crank-angle-resolved in-cylinder sampling techniques and fast-response emission analysers. Furthermore, the ratio of nitric oxide to nitrogen dioxide under the LTC cycles has been quantified and compared with that in conventional diesel combustion. This paper intends to identify the major impacts of the hydrocarbons on the NO _x emission of diesel LTC cycles.