Gasoline Direct Injector Deposits: Impacts of Fouling Mechanism on Composition and Performance

Injector performance in gasoline Direct-Injection Spark-Ignition (DISI) engines is a key focus in the automotive industry as the vehicle parc transitions from Port Fuel Injected (PFI) to DISI engine technology. DISI injector deposits, which may impact the fuel delivery process in the engine, sometimes accumulate over longer time periods and greater vehicle mileages than traditional combustion chamber deposits (CCD). These higher mileages and longer timeframes make the evaluation of these deposits in a laboratory setting more challenging due to the extended test durations necessary to achieve representative in-use levels of fouling. The need to generate injector tip deposits for research purposes begs the questions, can an artificial fouling agent to speed deposit accumulation be used, and does this result in deposits similar to those formed naturally by market fuels?

In this study, a collection of DISI injectors with different types of conditioning, ranging from controlled engine-stand tests with market or profould fuels, to vehicle tests run over drive cycles, to uncontrolled field use, were analyzed to understand the characteristics of their injector tip deposits and their functional impacts. The DISI injectors, both naturally and profouled, were holistically evaluated for their spray performance, deposit composition, and deposit morphology relative to one another. The testing and accompanying analysis reveals both similarities and differences among naturally fouled, fouled through long time periods with market fuel, and profouled injectors, fouled artificially through the use of a sulfur dopant. Profouled injectors were chemically distinct from naturally fouled injectors, and found to contain higher levels of sulfur dioxide. Also, profouled injectors exhibited greater volumes of deposits on the face of the injector tip. However, functionally, both naturally-fouled and profouled injectors featured similar impacts on their spray performance relative to clean injectors, with the fouled injector spray plumes remaining narrower, limiting plume-to-plume interactions, and altering the liquid-spray penetration dynamics, insights from which can guide future research into injector tip deposits.