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A range of gasoline/alcohol blends containing methanol, ethanol, iso-propanol and n-propanol, up to 5% oxygen content by mass, was tested in a multi-valve production engine to quantify the raw exhaust emissions, performance and burn-rate. A heat-release model was developed to facilitate the quantification of burn-rate. The engine was operated with various control strategies to enable the results to represent the response of different engine types. With standard open-loop engine calibration the alcohols reduced the equivalence ratio which resulted in increased combustion duration and reduced regulated emissions, while there was no difference between the effects of the different alcohols.

The Motor Octane Number (MON) ranks fuels by their chemical resistance to knock. Evaporative cooling coupled with fuel chemistry determine Research Octane Number (RON) antiknock ratings. It is shown in this study that fuel Octane sensitivity (numerically RON minus MON) is linked to an important difference between the two test methods; the RON test allows each fuel's evaporative cooling characteristics to affect gas temperature, while the MON test generally eliminates this effect by pre-evaporation. In order to establish RON test charge temperatures, a computer model of fuel evaporation was adapted to Octane Engine conditions, and simulations were compared with real Octane Test Engine measurements including droplet and gas temperatures. A novel gas temperature probe yielded data that corresponded well with model predictions. Tests spanned single component fuels and blends of isomers, n-paraffins, aromatics and alcohols.

A procedure is described to estimate the influence of end-gas temperature on Octane Number. Blending methanol with gasoline is known to cause a disproportionate increase in Research Octane Number, and this is found to correlate well with the evaporative cooling characteristics of these blends. The Motor Octane Number test eliminates evaporative effects, and the difference between the two test methods is evaluated in terms of evaporative cooling. It is concluded that the high heat of vaporization of methanol is largely responsible for the excellent RON performance of methanol-gasoline blended fuels.

A computer model of fuel evaporation in an idealized intake system is used to study the effect of engine speed on air-fuel mixture temperatures. The model allows for multi-component fuels present both as entrained droplets and wall films. Data are presented showing the relative importance of a range of parameters including: fuel composition, air speed, and droplet size and distribution. Computer predictions are compared with empirical data gathered using various methanol-gasoline blends on a test-rig. Model predictions are found to correlate significantly with measured film and droplet temperature data.

The results of an investigation into intake system fuel evaporation are used to study the influence of engine speed on fuel anti-knock performance. It is found that, while adding methanol to gasoline causes dramatic cooling at low engine speeds, this relative effect is lost at higher speeds, primarily due to lower residence times. At low speeds, the cooling inhibits knock for methanol-gasoline blends. However, at high speeds, these blends are found to lose this relative advantage, removing the knock inhibition provided by cooling, and this facilitates knocking at high speeds.