An analysis of spray development with iso-octane, n-pentane, gasoline, ethanol and n-butanol from a multi-hole injector under hot fuel conditions

High-pressure multi-hole injectors for direct-injection spark-ignition engines offer some great benefits in terms of fuel atomisation, as well as flexibility in fuel targeting by selection of the number and angle of the nozzle’s holes. However, very few data exist for injector-body temperatures representative of engine operation with various fuels, especially at low-load conditions with early injection strategies that can also lead to phase change due to fuel flash boiling upon injection. The challenge is further complicated by the predicted fuel stocks which will include a significant bio-derived component presenting the requirement to manage fuel flexibility. The physical/chemical properties of bio-components, like various types of alcohols, can differ markedly from gasoline and it is important to study their effects in direct comparison to liquid hydrocarbons. This work outlines results from an optical investigation (high-speed imaging and droplet sizing) into the effects of fuel properties, temperature and pressure conditions on the extent of spray formation. Specifically, gasoline, iso-octane, n-pentane, ethanol and n-butanol were tested at 20, 50, 90 and 120 °C injector body temperatures for ambient pressures of 0.5 bar and 1.0 bar in order to simulate early homogeneous injection strategies for part-load and wide open throttle engine operation; some test were also carried out at 180 °C, 0.3 bar. Droplet sizing was also performed for gasoline, iso-octane and n-pentane using Phase Doppler and Laser Diffraction techniques in order to understand the effects of low- and high-volatility components on the atomisation of the multi-component gasoline. The boiling points and distillation curves of all fuels, their vapour pressures and bubble points, as well as density, viscosity and surface tension were obtained and the Reynolds, Weber and Ohnesorge numbers were considered in the analysis.