Preignition Behavior of n-Heptane, iso-Octane, and Propionaldehyde Blends in a Pressurized FlowReactor

摘要

Autoignition and reactivity behavior in engines is affected by both the incoming fuel/air charge and the finaland the partial oxidation products left in the cylinder from the previous cycle. In the present study propionaldehydewas selected as a representative aldehydic partial oxidation product, and it was added to n-heptane/iso-octaneblends to examine the effect on the preignition reactivity behavior. The test fuels were reacted in a pressurizedflow reactor operated over a range of reaction temperatures covering preignition conditions, and the extent ofreaction was determined from extracted samples using standard online analyzers to measure CO and CO2 andtotal hydrocarbons. For simple mixtures of n-heptane and iso-octane, holding n-heptane constant, the addition ofiso-octane narrows the temperature range of low and intermediate temperature reactivity; however, maximum COconcentration and the temperature of this maximum are essentially unchanged. These results can not be simplyinterpreted by the role of iso-octane as a scavenger of OH radical. When propionaldehyde is added, the reactivityof n-heptane and iso-octane in the low temperature region (< 650 K) is reduced. However, in the intermediatetemperature region (700 – 900 K) the propionaldehyde contributes to the overall reactivity and reduces the NTCbehavior, which can lead to an earlier hot ignition. The kinetic implications of this behavior are discussed in thepaper.