Evaporating characteristics of diesel sprays under split-injection condition with a negative dwell time

Abstract

This paper investigates the effects of the split-injection strategy with a negative dwell time using a multi-hole diesel injector under evaporating conditions. To compare with negative dwell conditions, the single-injection and positive and zero dwell conditions were adopted. The Laser Absorption Scattering (LAS) technique was employed to measure the temporal and spatial evolution of fuel evaporation and mixture concentration in the experiments. The split injection of 7:3 was selected according to the results of the previous study that proposed a homogeneous mixture after the end of injection. The dwell times of −50 us, 0 us, and 120 us were selected based on the measurement of the injection rate. The blended fuel consisting of 97.5% of n-tridecane and 2.5% of 1-methylnaphthalene in volume was used. The results show that a shorter spray tip penetration was present in the split injection with a negative dwell time. This phenomenon is expected to reduce the possibility of wall impingement and result in fewer nitrogen oxides (NOx) and unburned hydrocarbons (UHCs) under the injection conditions with a negative dwell time, especially for the conditions of a large injection amount and small-bore engines. Moreover, different spray shapes and behavior occurred in the case of different injection strategies. The spray of split-injection strategy with a negative dwell time has large radial dispersion, and it can improve the air utilization inside a cylinder.

Keywords

• Diesel spray
• Split injection
• Negative dwell
• Evaporating