Three-stage autoignition of gasoline in an HCCI engine: An experimental and chemical kinetic modeling investigation

Abstract

The alternative HCCI combustion mode presents a possible means for decreasing the pollution with respect to the conventional gasoline or diesel engines, while maintaining the efficiency of a diesel engine or even increasing it. This paper investigates the possibility of using gasoline in an HCCI engine and analyses the auto-ignition of gasoline in such an engine. The compression ratio that has been used is 13.5, keeping the inlet temperature at 70 °C, varying the equivalence ratio from 0.3 to 0.54 and the EGR (represented by N 2 ) ratio from 0 to 37 vol%. For comparison, a PRF95 and a surrogate containing 11 vol% n-heptane, 59vol% iso-octane and 30 vol% toluene are used. A previously validated kinetic surrogate mechanism is used to analyze the experiments and to yield possible explanations to kinetic phenomena. From this work, it seems quite possible to use the high octane-rated gasoline for auto-ignition purposes, even at lean inlet conditions. Furthermore, it appeared that gasoline and its surrogate, unlike PRF95, shows a three-stage auto-ignition. Since the PRF95 does not contain toluene, it is suggested by the kinetic mechanism that the benzyl radical, issued from toluene, causes this so-defined "obstructed pre-ignition" and delaying thereby the final ignition for gasoline and its surrogate. The results of the kinetic mechanism supporting this explanation are shown in this paper.

Premixed ignition characteristics of blends of gasoline and diesel-like fuels on a rapid compression machine

“…Although the pure gasoline contains relatively small amount of long straight molecules (n-heptane), its pressure trace still features a two-stage increase, which agrees with previous researches [11]. Machrafi and Cavadias [12]. found that the homogenous charge compression ignition combustion has three heat release stages: they are the cool flame reactions by long straight molecules such as n-heptane, the obstructed preignition by the formation of benzyl radical from aromatics such as toluene, and the main heat release stage [12].…”

“…Machrafi and Cavadias [12]. found that the homogenous charge compression ignition combustion has three heat release stages: they are the cool flame reactions by long straight molecules such as n-heptane, the obstructed preignition by the formation of benzyl radical from aromatics such as toluene, and the main heat release stage [12]. The two heat release …”

Experimental validation of concentration profiles in an HCCI engine, modelled by a multi-component kinetic mechanism: Outline for auto-ignition and emission control

“…Considering these observations, the aim of this paper can be divided in two parts. The first is to validate experimentally the reduced kinetic mechanism against experimental concentration profiles with the use of an HCCI engine [20,21,42]. In this study, the experimental concentration profiles are extracted from [43] and reconverted from ppmC into ppmv.…”

Global reaction mechanism for the auto-ignition of full boiling range gasoline and kerosene fuels

“…For branched aromatics, however, the situation is different. For toluene for example, several researchers [51,52] reported that the toluene molecule reacts with OH to form the relatively stable benzyl radical and hereby acts as a sink for the OH radicals which in a pure alkanic fuel blend induce the second-stage ignition. Both these phenomena reduce the cool flame and overall reactivity and hence delay the second-stage ignition.…”