HCCI engine modeling and experimental investigations - Part 2: The composition of a NO-PRF interaction mechanism and the influence of NO in EGR on auto-ignition

摘要

This article presents an investigation of the effect of NO in EGR on HCCI auto-ignition, by means of experiments and a NO-PRF interaction mechanism. The influence is investigated both numerically and experimentally. The numerical part is effected by a composition of a NO submechanism and the subsequent addition of this sub mechanism to a reduced validated n-heptane/iso-octane PRF mechanism, the latter of which is presented in a previous article, named article 1 (Machrafi et al., submitted 2006). The experimental part is effected on a CFR engine, operating at HCCI conditions, with an inlet temperature of 70 degrees C and a compression ratio of 10.2. Hereby n-heptane and PRF40 are used as the fuels, using different equivalence ratios in order to extend the interpretation domain. The NO adding concentration is experimentally varied between 0 and 160 ppm. The results showed that adding NO at low concentrations advances the ignition delays, the promoting reactions being more reactive than the inhibitory ones. The promoting effect seems to be at its maximum at an addition of 45 ppm concerning the fuel PRF40. At higher adding concentrations of NO the promoting effect becomes less and the inhibitory reactions become more reactive. The effect of NO on the auto-ignition of n-heptane seemed, however, to be unsignificant. The effect of NO was qualitatively well represented by the mechanism, while quantitatively the mechanism predicted a lower effect of NO at an addition of 45 ppm.