Fuel Ignition Delay Maps for Molecularly Controlled Combustion

Abstract

Molecularly controlled combustion systems (MCCSs) combine the advantages of compression-ignition and sparkignition engines by employing both a low reactivity fuel and a high reactivity fuel (HRF). To optimize the MCCS, fuels must be tailored to the engine requirements with respect to fuel reactivity. We aim at deriving requirements for HRFs and identification of suitable HRF candidates. Single-cylinder experiments are performed to assess the suitability of conventional reactivity indicators for MCCS. Fuel ignition delay time (IDT) maps are proposed as alternative reactivity indicators conveying more information. The maps are constructed through five representative IDT measurements at varying temperatures and pressures within the constant volume combustion chamber of the advanced fuel ignition delay analyzer (AFIDA). Specifically, the IDT maps cover the temperature and pressure range of 500−700 °C and 10−35 bar, respectively; and the IDT is measured at the four corner points of that range and the center point. We present measured IDT maps for more than 50 oxygenated and nonoxygenated hydrocarbon species and analyze suitability for MCCSs, e.g., 1,3-dioxane and 1-heptanol are found as possible HRF. The measurement data are further utilized to develop a graph neural network (GNN) model that can predict IDT maps directly from the molecular structure with high accuracy, constituting a first step toward in-silico screening of HRFs for MCCSs.