Enhancing -sensitivity of ignition delay times through dilution of fuel-air mixture

The high phi-sensitivity (eta) of ignition delay time (tau IDT) is one of the desirable fuel properties for the high-load extension of advanced compression ignition engine. Recent studies revealed the effectiveness of a high dilution rate (x(D)) for enhancing eta at the engine-relevant conditions. This study aims to quantify the effect of dilution on the eta of isooctane using a combined experiment-simulation approach. The ignition delay of the isooctane/air mixture was measured with an Advanced Fuel Ignition Delay Analyzer (AFIDA) over the temperature range of 623 - 923 K at 10 bar pressure with global phi = 0.3 - 0.6, with and without 28.6% of additional N-2 dilution. For precise evaluation of experimental eta, the facility effect of the AFIDA experiment was characterized with three-dimensional computational fluid dynamics (3-D CFD) simulation. The temperature in the combustion chamber from 3-D CFD indicated a substantial temporal dependency, varying up to similar to 52 K by charge-cooling of fuel injection and heat transfer from the wall. We introduced the dimensionless number theta(t) for characterizing the temporal profile of chamber temperature. Consideration of the facility effect using theta(t) resulted in better agreement between the experimental eta and zero-dimensional (0-D) kinetics simulation. The refined. were then further utilized to quantify the effectiveness of dilution to eta. The extent of eta enhancement with dilution strategy was maximized at the low-temperature chemistry regime, increasing eta by 77% with a 28.6% dilution rate. Further analysis on the dilution effect was carried out using 0-D kinetics simulation, revealing the critical dimensionless numbers relevant to the effectiveness of dilution to eta enhancement. This study is the first experiment-simulation combined research to quantify the effect of dilution on eta, facilitating the kinetics model refinement for better reproduction of phi-sensitivity. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.