Injector Fouling and Its Impact on Engine Emissions and Spray Characteristics in Gasoline Direct Injection Engines

Abstract

Unlike in port fuel injection (PFI) systems, gasoline direct injection (GDI) engines deliver fuel directly into the combustion chamber. This opens up the possibility of new injection strategies and can improve efficiency and fuel consumption, especially under partial load [1,2,3]. An additional advantage is the so-called stratified charge operation, which allows adjustment of the injection and ignition timings of the engine, to further optimise engine operation [4]. In addition, the charge cooling effect observed during fuel injection allows for the use of higher compression ratios, with reduced risk of knocking. These benefits are gaining more attention with the continuing trend of downsizing and super-or turbocharging of engines, due to increasingly strict emissions regulations [5,6,7]. Additional benefits of GDI are the option to completely shut-off fuel supply while coasting [8] and improved cold start behaviour compared to PFI engines [9,10].One major challenge of the GDI concept, however, is the potential for increased formation of particulate emissions. Recent emissions legislations such as EURO 6 in Europe and LEV III (Low Emissions Vehicle Program) in the US pose very strict limitations on particle number and mass (PM) concentrations [11,12]. Methods to control particulate emissions from GDI engines are therefore important.Introduction of an injector into the combustion chamber of a GDI engine results in direct exposure of the injector tip to the harsh conditions occurring during combustion. Because the flame directly interacts with the nozzle, combustion products can be deposited on the surface and inside cavities. This is usually referred to as injector fouling or coking and can have an adverse effect on fuel consumption, engine performance and both hydrocarbons and particulate emissions. Formation of deposits on the injector tip can result in alteration of spray pattern leading to increased spray impingement and therefore increased particulate emissions [13,14,15,16].The phenomenon of injector fouling and how it is influenced by fuel and engine parameters was the focus of a number of studies. Aradi et al. [17] investigated different fuel blends under several conditions in a four cylinder engine. They used rich fuel-to-air ratios in order to promote fouling. By measuring the temperature of the injector tip with an internal sensor, they saw that with increasing temperature Injector Fouling and Its Impact on Engine Emissions and Spray Characteristics in Gasoline Direct Injection Engines ABSTRACTIn Gasoline Direct Injection engines, direct exposure of the injector to the flame can cause combustion products to accumulate on the nozzle, which can result in increased particulate emissions. This research observes the impact of injector fouling on particulate emissions and the associated injector spray pattern and shows how both can be reversed by utilising fuel detergency. For this purpose multi-hole injectors were deliberately fouled in a four-cylinder test engine with two different base fuels. During a fo...

The process of tip wetting at the spray injection end

“…In gasoline direct injection (GDI), tip coking can generate a progressive tip sooting that is a large source of particles. [1][2][3] High-magnification and spectrally filtered images of the injector tip showed a high probability of soot formation near the injector tip and also showed an increased probability of hard soot on the injector surface compared to inside the nozzle holes. 1,4 To our knowledge, very limited work has been published in the field of multi-hole direct injection tip wetting as a main factor of the tip coking then fouling, and no clear and detailed process has been proposed up to now.…”

Recent Progress in Automotive Gasoline Direct Injection Engine Technology

“…In addition, Jiang's work found that the penetration length and mean droplet size of each jet were increased significantly, in contrast to Song's observations. An increased penetration length was also observed by Henkei et al [134]. Wang et al [69] indicated that deposits inside the counter bore could restrict air recirculation and entrainment, leading to lower exiting turbulent kinetic energy of the spray from a coked injector and producing a larger mean droplet size.…”

“…Results obtained by Wen et al [137] with a GDI vehicle having a mileage of 13,000 km showed that particulate mass and fuel consumption were increased by 376 and 3.02%, respectively, compared with the values obtained using fresh injectors. In addition, gaseous emissions such as THC, non-methane hydrocarbon (NMHC) and NOx increased by 17.1, 24.5 and 23.4%, respectively, and PN emissions could be increased by several orders of magnitude [133,134]. The fuel stored in the fouled injector tip deposits during injection and then released later caused diffusive combustion events and thus increased PM and PN emissions [112].…”

An adsorption-precipitation model for the formation of injector external deposits in internal combustion engines

“…Investigations of the effect of injector deposits on the injector performance and thermal conditions are scarce [8,17,[80][81][82]. As a result, the mechanism of their adverse action is not completely understood.…”