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Lean-burn Spark Ignition Direct Injection (SIDI) engines offer potential fuel economy savings, however, lack of cost-effective lean NOx aftertreatment systems has hindered its broad application. Lean NO Trap (LNT) and Urea Selective Catalytic Reduction (SCR) technologies have been widely investigated as possible solutions, but they both have considerable drawbacks. LNT catalysts suffer from high Platinum Group Metals (PGM) cost, poor thermal durability, sulfur poisoning and active SO regeneration requirements. Urea SCR systems require a secondary fluid tank with an injection system, resulting in added system cost and complexity. Other concerns for urea SCR include potential freezing of the urea solution and the need for customers to periodically fill the urea reservoir. In this paper we report a low-cost, high efficiency concept that has the potential to be a key enabler for lean-burn gasoline engines.

This study was undertaken to determine the vapor pressure characteristics of M85 fuel, a mixture of 85 percent methanol and 15 percent gasoline or other hydrocarbons. For M85 fuels made with full-boiling-range gasolines, the vapor pressure of the M85 fuel at 37.8°C increased linearly with an increase in the vapor pressure of the gasoline. A different linear relationship was obtained for M85 fuels made with pure hydrocarbons rather than with gasolines. The vapor pressure of an M85 fuel was higher when the hydrocarbon component was a pure hydrocarbon or simple hydrocarbon mixture rather than a gasoline of the same vapor pressure. Vapor pressure vs. temperature characteristics were measured for a number of M85 fuels and the hydrocarbons from which they were made. In most cases, a change in temperature caused a greater change in the vapor pressure of the M85 fuel than in the vapor pressure of the hydrocarbon component of the M85.

We have developed and validated a simple, quick, in-expensive method for determining the methanol or hydrocarbon content of a methanol blend fuel (a mixture of methanol and gasoline). The method exploits the insolubility of water in hydrocarbons. Briefly, 50 mL of fuel is mixed with a like amount of water and allowed to settle; the volume of the upper phase is directly correlated to the amount of hydrocarbon in the fuel. Equations and graphs are provided which translate between the hydrocarbon volume measured and the methanol content or the hydrocarbon content of the fuel. This method and the graphs and equations in this report are valid for methanol fuels made with any gasoline or virtually any hydrocarbon mixture, provided there are not oxygenates such as ethanol or MTBE present in the hydrocarbon fraction. The accuracy and precision of the method are excellent, for mixtures of dry methanol and oxygenate free gasoline.

Laboratory bench tests were conducted to simulate both the diurnal and the hot-soak (carburetor only) parts of an evaporative emissions test with gasolines containing various alcohols and ethers. The mass of vapor generated during each test and the detailed composition of the vapor were determined for each fuel. Using published atmospheric reactivity scales, the ozone-forming potential of the vapor was estimated. Based on the scale of maximum incremental reactivities, which the California Air Resources Board has proposed for future emissions standards, the diurnal test results showed that the addition of methyl tertiary-butyl ether (MTBE) or ethyl tertiary-butyl ether (ETBE) to gasoline resulted in about the same or lower total vapor reactivity compared to the gasoline alone.

Ethyl tertiary-butyl ether (ETBE), a reaction product of ethanol and isobutylene, has been proposed as a high-octane blending component for gasoline. Laboratory studies have been conducted to determine how the addition of ETBE to gasoline affects the volatility characteristics of the fuel, and how the effects of ETBE compare with those of the commonly used oxygenates, ethanol and MTBE. The amount of vapor generated in bench-scale simulated evaporative emissions tests with each of those three oxygenates was also determined. The vapor pressures of gasoline-ETBE blends decreased linearly as the concentration of ETBE was increased. In contrast, ethanol addition raises the vapor pressure of gasoline, although in a nonlinear fashion. ETBE increased the mid-range volatility of the fuel, in the same way as a pure hydrocarbon of similar vapor pressure and boiling point.

An investigation was conducted to determine the change in Reid vapor pressure (RVP) which results when gasoline and various gasoline-alcohol blends are mixed. Such mixing occurs in vehicle fuel tanks when a motorist buys gasolines and blends alternately. When mixing a gasoline with a gasoline-alcohol blend of the same RVP, the resulting mixture always had a higher RVP, due to the non-linear effect of alcohol concentration in gasoline on RVP. Even when a blend had a much lower RVP than gasoline, some mixtures of the two still had higher RVP's than the gasoline. When two common commercial blends, 10 percent ethanol and 10 percent Oxinol™ 50, both having the same RVP, were mixed in various proportions there was essentially no change in RVP. The results of this study suggest that the presence of both gasolines and blends in the marketplace can lead to higher in-use evaporative emissions from vehicles, even if the blends meet the same volatility standards as gasoline.