The Heavy Duty Gasoline Engine - A Multi-Cylinder Study of a High Efficiency, Low Emission Technology 2005-01-1135

SwRI has developed a new technology concept involving the use of high EGR rates coupled with a high-energy ignition system in a gasoline engine to improve fuel economy and emissions. Based on a single-cylinder study [1], this study extends the concept of a high compression ratio gasoline engine with EGR rates > 30% and a high-energy ignition system to a multi-cylinder engine. A 2000 MY Isuzu Duramax 6.6 L 8-cylinder engine was converted to run on gasoline with a diesel pilot ignition system. The engine was run at two compression ratios, 17.5:1 and 12.5:1 and with two different EGR systems - a low-pressure loop and a high pressure loop. A high cetane number (CN) diesel fuel (CN=76) was used as the ignition source and two different octane number (ON) gasolines were investigated - a pump grade 91 ON ((R+M)/2) and a 103 ON ((R+M)/2) racing fuel.

The results showed that the stock, 17.5:1 compression ratio (CR) was unsuitable for operation except at light (<50%) loads with the peak BMEP's of 700 kPa on 91 ON fuel and 1000 kPa on 103 ON fuel. The engine-out BSNOx ranged from 0.76 to 2.35 g/kW-hr with brake thermal efficiencies (BTE) between 26-38% over the load range. At 12.5:1 CR, the peak BMEP's were much higher, 1260 kPa on 91 ON and 1720 kPa on 103 ON. The engine-out BSNOx ranged from 0.03 to 2.10 g/kW-hr with BTE's between 23-37% over the load range. With the addition of a 3-way catalyst, made possible by stoichiometric operation, the possibility exists for extremely low emissions at diesel-like fuel economies. These results show that the technology has the potential to return the efficiency of a modern diesel engine (equipped with aftertreatment devices) with the low emissions of a light-duty gasoline engine.