A New Approach to Ethanol Utilization: High Efficiency and Low NOx in an Engine Operating on Simulated Reformed Ethanol 2008-01-2415

The use of hydrogen as a fuel supplement for lean-burn engines at higher compression ratios has been studied extensively in recent years, with good promise of performance and efficiency gains. With the advances in reformer technology, the use of a gaseous fuel stock, comprising of substantially higher fractions of hydrogen and other flammable reformate species, could provide additional improvements. This paper presents the performance and emission characteristics of a gas mixture of equal volumes of hydrogen, CO, and methane. It has recently been reported that this gas mixture can be produced by reforming of ethanol at comparatively low temperature, around 300C. Experiments were performed on a 1.8-liter passenger-car Nissan engine modified for single-cylinder operation. Special pistons were made so that compression ratios ranging from CR= 9.5 to 17 could be used. The lean limit was extended beyond twice stoichiometric (up to lambda=2.2). Manifold conditions, operating temperatures, and spark-timing were controlled, and cylinder pressure and NOx emissions recorded.

Test results of using the gaseous reformates were compared to those at baseline conditions using gasoline and the use of liquid ethanol. Net indicated efficiency of the engine almost doubled, reaching 46% at lambda=2 at CR=17. Most of the efficiency improvement was due to lean operation. Further improvement was realized by increasing compression ratios through CR=13, with smaller gains at still higher compression ratios. The improvement due to lean operation was approximately linear with air-fuel ratio - deteriorating sharply beyond the lean limit. There was no noticeable knock at all compression ratios with the gas mixture, so the engine power could be maintained throughout the operating range tested. The impact of lean operation of the reformate gaseous fuel on NOx emissions was favorable. These results suggest new opportunities for the more efficient and alternative utilization of biofuel feedstocks.