Terry Alger

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.

Ethanol Flex-fuel Engine Improvements with Exhaust Gas Recirculation and Hydrogen Enrichment

An investigation was performed to identify the benefits of cooled exhaust gas recirculation (EGR) when applied to a potential ethanol flexible fuelled vehicle (eFFV) engine. The fuels investigated in this study represented the range a flex-fuel engine may be exposed to in the United States; from 85% ethanol/gasoline blend (E85) to regular gasoline. The test engine was a 2.0-L in-line 4 cylinder that was turbocharged and port fuel injected (PFI). Ethanol blended fuels, including E85, have a higher octane rating and produce lower exhaust temperatures compared to gasoline. EGR has also been shown to decrease engine knock tendency and decrease exhaust temperatures. A natural progression was to take advantage of the superior combustion characteristics of E85 (i.e. increase compression ratio), and then employ EGR to maintain performance with gasoline. When EGR alone could not provide the necessary knock margin, hydrogen (H2) was added to simulate an onboard fuel reformer. This investigation explored such a strategy at full load, and examined the potential of EGR for ethanol blends at part and full load. This investigation found the base engine torque curve could be matched across the range of fuels at a higher compression ratio. The engine could operate at maximum brake torque (MBT) timing at full load for all but the lowest octane fuel. Fuel enrichment was not needed to control exhaust temperatures, whereby carbon monoxide emissions were drastically reduced. Full load fuel consumption was reduced by 8-10% with regular gasoline (92 RON) and 20-21% with premium (100 RON). Full load brake thermal efficiency (BTE) increased 9.3 percentage points with E85 compared to the base engine. The full load fuel consumption was only 9% higher than the baseline engine even though E85 has ~25% lower energy content (net heat of combustion) than gasoline.