Abstract
Research and/or Engineering Questions/Objective
Injector fouling in GDI (gasoline direct injection) engines is associated with obstruction of fuel flow from injector holes, alteration of injector spray targeting and ultimately combustion inefficiencies resulting in, for example, higher particulate emissions. In this study we investigate the use of fuel with detergent additive to reduce injector tip deposits and therefore improve combustion efficiency.
Methodology
A four cylinder GDI engine was operated using three different base fuels, which were partly dosed with detergent additive. In total six different fuels were tested. The engines were tested for four hours (test cycle 1) and the PM/PN emissions in the exhaust gas were monitored over time for the duration of the test. After test cycle 1 the injectors were removed and replaced by new injectors. Test cycle 2 was then conducted under identical conditions to 1. Without removing the injectors from test cycle 2, a third test cycle (3) was then operated again under the same conditions but using only detergent containing fuels. Micrographs of the injectors from test cycles 1 and 3 were recorded.
Results
During test cycles 1 and 2, the engines that operated with the two detergent containing fuels showed no increase in PM/PN emissions above ambient levels during the run time of the experiment. The exhaust from the engines operated on fuels with no detergent showed significant particulate emissions of the magnitude 106 PN in 1/cm-3 and PM values up to 0.4 mg/m³. In test cycle 3 all the engines from test cycle 2 were operated with detergent containing fuels. After 10 hours the PM/PN emissions from all engines either remained at or decreased to ambient air concentrations with the exception of the ethanol containing fuel which decreased by 40 % relative to the end of test cycle 2. Microscopy showed that the engines running with higher particulate emissions had more injector-hole deposits compared to the engines running with ambient levels of particulate emissions. After test cycle 3 the deposits were less severe.
Limitations of this study
A limitation of this study is the indirect measurement of injector deposits over the engine test cycles. We assume a link between particulate emissions and injector deposits based on earlier studies. Direct observation of the injector spray during engine operation would help to determine if increased injector fouling does indeed result in altered spray characteristics.
What does the paper offer that is new in the field in comparison to other works of the author?
We use particulate emissions as a measure of injector fouling during an engine test cycle. Demonstration of the reduction of deposits and therefore particulate emissions by detergent containing fuels from the beginning of engine operation is achieved.
Conclusions
We show that detergent containing fuels decrease PM/PN emissions from GDI engines containing fouled injectors and this is most likely achieved by deposit reduction at the injector tip holes. This experiment demonstrates the ability of detergency to improve combustion efficiency in an engine. The fouling of GDI injectors with detergent free fuels occurs rapidly over a four hour engine test cycle. The clean-up effects of detergent containing fuels are observed over a 10 hour test cycle under the same engine operating conditions.
Key Words : Direct Injection, Gasoline, Deposits, Detergent