Characterisation of a Bio-Ethanol Direct Injection Spray Under Sub-Zero Conditions

Due to current dependence on depleting fossil fuel reserves, alternative fuels are being considered particularly for the transport sector. Suitable replacement fuels for gasoline are bio-fuels such as bio-ethanol. One of the obstacles preventing the wider use of pure bio-ethanol is its volatility which causes problems at low temperatures. To over come this, blends of bio-ethanol and gasoline - such as E85 (85 % ethanol and 15 % gasoline), are used which have increased volatility thereby increasing reliability during cold starts and running [1]. The addition of gasoline reduces the corrosive nature of ethanol by decreasing the amount of water absorbed by the resulting fuel. A lower air-to-fuel ratio is also required during cold start, thus increasing Unburnt Hydrocarbons (UBHC) and Carbon Monoxide (CO). This can be mitigated by exhaust after treatment systems; however the low system temperatures occurring during cold start and warm up cycles severely limits the effectiveness of these systems. This leads to an increase in UBHC and CO emissions of up to 15 times at -20 o C compared to that at 23 o C for gasoline G-DI engines [2]. The objective of this study is to assess the influence of sub-zero fuel temperatures on spray characteristics such as droplet size, velocity and spray pattern of E85 compared to gasoline sprays. Fuel temperatures as low as 243 K (-30 o C) were achieved. The data presented and analysed in this paper were obtained using a temporally and spatially resolved Phase Doppler Anemometry (PDA) system from fuel injections by a piezo controlled G-DI injector mounted in a constant volume, optical experimental facility. The results are presented in terms of the spray kinematics and spray quality and are discussed and analysed through comparison with the benchmark spray at atmospheric conditions.