Auto-ignition of direct injection spray of light naphtha, primary reference fuels, gasoline and gasoline surrogate

Abstract

In this work, the spray and auto-ignition characteristics of light naphtha (LN), primary reference fuels (PRF65, PRF95), Haltermann gasoline (CARB LEVIII, 10 vol% ethanol), and a gasoline surrogate were studied in an optically accessible constant volume combustion chamber. An outwardly opening hollow cone piezoelectric gasoline direct injection fuel injector was used. Five ambient temperatures from 650 to 950 K with a 75 K step were selected with a fixed ambient density of 3.5 kg/m3, similar to the Spray G density defined by the engine combustion network (ECN). Fuel auto-ignition was achieved with varying ignition delays for the five investigated fuels depending on the selected experimental conditions. Results show that the auto-ignition locations are randomly distributed in the combustion chamber. Differences in ignition delay times among the five fuels are more significant when the ambient temperature is lower than 750 K. When the ambient temperature is lower than 750 K, PRF95 always has the longest ignition delay and LN has the shortest. Ignition delays of the five fuels are almost identical when the ambient temperature exceeds 750 K. Meanwhile, the five fuels have a similar spray front penetration length and spray angles before the occurrence of auto-ignition under all the investigated conditions.