Charles E. Roberts

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

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 BMEPs 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 BMEPs 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 BTEs 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.

Cooled exhaust-gas recirculation for fuel economy and emissions improvement in gasoline engines:

Modern gasoline engines face fuel-efficiency challenges due to inherent limitations including knock, pumping losses, and fuel enrichment. The addition of exhaust-gas recirculation (EGR) has been shown to improve the fuel consumption of gasoline engines, either port fuel injected or direct injected, by reducing pumping losses and knock and eliminating the enrichment region. In addition, the use of EGR has been shown to substantially reduce emissions of nitrogen oxides (NO x ) and CO. A 2.4-litre multi-point injection engine and a 1.6-litre gasoline direct injection engine were run with high levels of both cooled and uncooled EGR. Unlike numerous previous publications, these engines included a modified ignition system that allows extension of the cooled EGR limit of the engine to greater than 25 per cent and improves combustion at lower EGR levels. The results showed that an improvement of between 5 and 30 per cent in fuel consumption is possible, with the largest improvement occurring in the typical enrichment region. In addition, the results showed that EGR can reduce knock, resulting in an improvement in combustion phasing. Finally, the high levels of EGR reduced the emissions of CO by 30 per cent and of NO x by up to 80 per cent. A detailed effort has been made to quantify the sources of improvement throughout the engine cycle and to demonstrate an EGR strategy (cooled EGR at high loads, internal EGR at low loads) that will maximize fuel consumption improvements. The results presented here indicate that the use of EGR in gasoline engines has the potential to reduce fuel consumption and emissions in a very cost-effective manner.

The Heavy-Duty Gasoline Engine - An Alternative to Meet Emissions Standards of Tomorrow

A technology path has been identified for development of a high efficiency, durable, gasoline engine, targeted at achieving performance and emissions levels necessary to meet heavy-duty, on-road standards of the foreseeable, future. Initial experimental and numerical results for the proposed technology concept are presented. This work summarizes internal research efforts conducted at Southwest Research Institute. An alternative combustion system has been numerically and experimentally examined. The engine utilizes gasoline as the fuel, with a combination of enabling technologies to provide high efficiency operation at ultra-low emissions levels. The concept is based upon very highly-dilute combustion of gasoline at high compression ratio and boost levels. Results from the experimental program have demonstrated engine-out NO x emissions of 0.06 g/hp/hr, at single-cylinder brake thermal efficiencies (BTE) above thirty-four percent. Multi-cylinder, 3-way catalyst equipped versions of this engine are estimated to provide NO x emissions of approximately 0.003 g/hp/hr at efficiencies approaching thirty-nine percent.

The Effect of Water on Soot Formation Chemistry

A combined, experimental and numerical program is presented. This work summarizes an internal research effort conducted at Southwest Research Institute. Meeting new, stringent emissions regulations for diesel engines requires a way to reduce NO x and soot emissions. Most emissions reduction strategies reduce one pollutant while increasing the other. Water injection is one of the few promising emissions reduction techniques with the potential to simultaneously reduce soot and NO x in diesel engines. While it is widely accepted that water reduces NO x via a thermal effect, the mechanisms behind the reduction of soot are not well understood. The water could reduce the soot via physical, thermal, or chemical effects. To aid in developing water injection strategies, this projects goal was to determine how water enters the soot formation chemistry. Linked burner experiments and modeling of a rich premixed flame were used to determine the magnitude of the thermal and chemical effect of water on soot formation and identify a possible kinetic mechanism to explain it. Following Decs model for diesel combustion processes (Dec, 1997; Flynn, et al., 1999) [1,19] , soot inception results from rich premixed combustion; thus the rich premixed flame provides an appropriate venue in which to isolate the influence of water on the kinetics. Open flame, burner experiments have been performed to quantify the soot inception point and the relative amounts of soot formation in premixed flames with and without water addition. These results have been used to expand and compliment data available in the published literature. Subsequent modeling has been used to predict trends in soot inception using currently accepted kinetic soot mechanisms. Results from this effort led to a revised kinetic mechanism for the process. Comparison of the experimental and modeling data has been used to assess the accuracy of soot formation mechanisms and ultimately has yielded a new understanding of the soot formation chemistry and the role of added water.

Measurement of Laminar Burning Velocity of Multi-Component Fuel Blends for Use in High-Performance SI Engines

A technique was developed for measuring the Laminar Burning Velocity (LBV) of multi-component fuel blends for use in high-performance spark-ignition engines. This technique involves the use of a centrally-ignited spherical combustion chamber, and a complementary analysis code. The technique was validated by examining several single-component fuels, and the computational procedure was extended to handle multi-component fuels without requiring detailed knowledge of their chemical composition. Experiments performed on an instrumented high-speed engine showed good agreement between the observed heat-release rates of the fuels and their predicted ranking based on the measured LBV parameters.