Effect of Ethanol Port-Fuel-Injector Position on Dual-Fuel Combustion in an Automotive-Size Diesel Engine

In contrast to the conventional approach of using ethanol in spark-ignition engines, this study demonstrates the potential of ethanol utilization in diesel engines using dual-fuel combustion, where ethanol is injected into the intake manifold and diesel is directly injected into the engine cylinder. The main focus is the effect of the ethanol port-fuel-injector (PFI) position on dual-fuel combustion and engine-out emissions. In this study, Mie-scattering spray imaging and engine tests were performed in an optical spray chamber simulating the intake manifold condition and a single-cylinder, automotive-size diesel engine, respectively. Two PFI positions are selected: one close to the hot intake valves, so that the sprays impinged upon the hot valve surface (position A), and the other further upstream of the intake valves, allowing increased residence time for interactions between ethanol droplets and intake airflow (position B). From ethanol spray images, it is suggested that the droplet size is smaller for PFI position B because of enhanced droplet-airflow interaction. However, the measured engine-out emissions show lower unburnt hydrocarbon and carbon monoxide emissions for PFI position A. This is argued to be due to reduced wall wetting because the surface boiling of ethanol droplets occurred on the hot valve seat and intake port wall. It is also found that the effect of the PFI position on global parameters, such as in-cylinder pressure, apparent heat release rate, and mean effective pressure, is much less significant than the effect of ethanol energy fraction. The maximum ethanol fraction is limited by misfiring associated with over-retarded combustion phasing. This limit is found to be higher for PFI position A because the wall-wetting is less problematic, consistent with the carbon monoxide and unburnt hydrocarbon emissions trend.