An experimental database on the effects of single- and split injection strategies on spray formation and spark discharge in an optical direct-injection spark-ignition engine fuelled with gasoline, iso-octane and alcohols

Abstract

This article presents results from a comprehensive optical study of a direct-injection spark-ignition research engine running on gasoline, iso-octane, ethanol, n-butanol and E10 fuels injected from a multi-hole central vertically positioned injector. The analysis was based on images of spray development, spark discharge and combustion to understand the effects of early and late injection strategies on in-cylinder phenomena. Specifically, `single'-injection strategies from early to late intake stroke as well as multiple `split' injection events with triple pulses in the early intake stroke or double pulses in the intake stroke and late compression stroke were investigated. The engine was run at 1500 r/min at part- and full-load conditions (0.5 and 1.0 bar inlet plenum pressure, respectively). Engine coolant temperatures of 20°C–90°C were employed to understand how fuel volatility was related to the phenomena observed. The sprays were imaged over a series of cycles primarily by laser sheet illumination on one vertical and two horizontal planes to identify three-dimensional aspects of the spray's development and its interactions with the incoming flow, valves, piston and liner. There was a clear fuel-impingement trade-off between early and late injection timings. The spark discharge was also imaged with all injection strategies and clear differences were observed. Selective combustion imaging provided insights into the flame's growth and motion with early and double early–late split injection strategies. The double earlylate injection strategy demonstrated the potential for control of the mixture formation and flow field over the early flame development stage of combustion.