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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.

Ethanol-blended gasoline fuels are penetratrating the market due to the renewable nature of ethanol and an anti-knock benefit associated with ethanol's higher octane number. Although ethanol usage is already popular in gasoline engines using port fuel injection (PFI), little fundamental information is available regarding important spray parameters. To address this issue, PFI sprays were studied in an optical chamber simulating boosted intake conditions. Using a high-resolution CCD camera, Mie-scattered spray images were obtained and processed to determine spray-tip penetration, mean droplet diameter, and number of droplets. The ethanol to gasoline ratio was varied to investigate effect of ethanol blending on these spray parameters.Mie-scattering imaging was also performed for various intake pressures considering turbocharged or supercharged conditions. From the experiments, expected trends were observed such as increasing tip penetration and decreasing mean droplet diameter with increasing time after the start of injection. Evidence of droplet breakup and evaporation during the spray penetration was also identified from detailed analysis of mean droplet diameters and number of droplets. Unexpected trends were also observed from ethanol sprays. Despite its lower vapor pressure, higher boiling point, and higher heat of vaporization, ethanol sprays showed a lower tip penetration and smaller droplet size than gasoline. The multi-component nature of conventional 3 gasoline was used to explain this trend: heavy molecules of gasoline breakup and evaporate at a slower rate than ethanol. It was also found that increased ambient pressure caused a shorter spray tip penetration due to higher ambient drag. By contrast, the mean droplet diameter was larger for higher ambient pressure because of decreased evaporation rate associated with increased saturation temperature. The fundamental information obtained in this study will help develop commercially viable ethanol-fuelled engines without compromising high power performance.

The present study aims to evaluate the effects of engine speed on gasoline compression ignition (GCI) combustion implementing double injection strategies. The double injection comprises of near-BDC first injection for the formation of a premixed charge and near-TDC second injection for the combustion phasing control. The engine performance and emissions testing of GCI combustion has been conducted in a single-cylinder light-duty diesel engine equipped with a common-rail injection system and fuelled with a conventional gasoline with 91 RON. The double injection strategy was investigated for various engine speeds ranging 1200~2000 rpm and the second injection timings between 12°CA bTDC and 3°CA aTDC. From the tests, GCI combustion shows high sensitivity to the second injection timing and combustion phasing variations such that the advanced second injection causes advanced combustion phasing and extended pre-combustion mixing time, and thereby increasing engine efficiency and decreasing ISFC. This leads to the reduced smoke/uHC/CO emissions but increased combustion noise and NO x emissions, similar to the trends in conventional diesel combustion. It is found that the increased engine speed requires a higher fuel mass per injection to maintain similar IMEP values, leading to lower efficiency, higher ISFC, and increased combustion noise. The heat release rate increases with increasing engine speed but the combustion phasing is largely unchanged. A typical smoke-NO x trade-off is found with increased smoke and decreased NO x emissions at higher engine speed, primarily due to reduced charge premixing time, which suggests the partially premixed charge-based GCI combustion behaves similar to conventional diesel combustion with overall lower smoke and NO x emissions.