Ethanol offers significant potential for increasing the compression ratio of SI engines resulting from its high octane number and high latent heat of vaporization. A study was conducted to determine the knock limited compression ratio of ethanol-gasoline blends to identify the potential for improved operating efficiency. To operate an SI engine in a flex fuel vehicle requires operating strategies that allow operation on a broad range of fuels from gasoline to E85. Since gasoline or low ethanol blend operation is inherently limited by knock at high loads, strategies must be identified which allow operation on these fuels with minimal fuel economy or power density tradeoffs. A single cylinder direct injection spark ignited engine with fully variable hydraulic valve actuation (HVA) is operated at WOT and other high-load conditions to determine the knock limited compression ratio (CR) of ethanol fuel blends. The geometric CR is varied by changing pistons, producing CR from 9.2 to 12.87. The effective CR is varied using an electro-hydraulic valvetrain that changed the effective trapped displacement using both Early Intake Valve Closing (EIVC) and Late Intake Valve Closing (LIVC). The EIVC and LIVC strategies result in effective CR being reduced while maintaining the geometric expansion ratio. It was found that at substantially similar engine conditions, increasing the ethanol content of the fuel results in higher engine efficiency and higher engine power. These results can be partially attributed to a charge cooling effect and a higher heating value of a stoichiometric mixture for ethanol blends (per unit mass of air). Additional thermodynamic effects on the ratio of specific heats (γ) and a mole multiplier are also explored. It was also found that high CR can increase the efficiency of ethanol fuel blends, and as a result, the fuel economy penalty associated with the lower energy content of E85 can be reduced by about twenty percent. Such operation necessitates that the engine be operated in a de-rated manner for gasoline, which is knock-prone at these high CR, in order to maintain compatibility. By using early and late intake valve closing strategies, good efficiency is maintained with gasoline, but peak power is about 33% lower than with E85.

Spark-ignition (SI) engines with direct-injection (DI) fueling can improve fuel economy and vehicle power beyond that of port fuel injection (PFI). Despite this distinct advantage, DI fueling often increases particle number emissions, such that SI exhaust may be subject to future particle emissions regulations. In this study, ethanol blends and engine operating strategy are evaluated for their effectiveness in reducing particle emissions in DI engines. The investigated fuels include a baseline emissions certification gasoline, a blend of 20 vol % ethanol with gasoline (E20), and a blend of 85 vol % ethanol with gasoline (E85). The operating strategies investigated reflect the versatility of emerging cam-based variable valve actuation technology capable of unthrottled operation with either early or late intake valve closing (EIVC or LIVC). Particle emissions are characterized in this study by the particle number size distribution as measured with a scanning mobility particle sizer (SMPS) and by the filter smoke number (FSN). Particle emissions for PFI fueling are very low and comparable for all fuels and breathing conditions. When DI fueling is used for gasoline and E20, the particle number emissions are increased by 1À2 orders of magnitude compared to PFI fueling, depending upon the fuel injection timing. In contrast, when DI fueling is used with E85, the particle number emissions remain low and comparable to PFI fueling. Thus, by using E85, the efficiency and power advantages of DI fueling can be gained without generating the increase in particle emissions observed with gasoline and E20.

<div class="section abstract"><div class="htmlview paragraph">Continued improvement in the combustion process of internal combustion engines is necessary to reduce fuel consumption, CO2 emissions, and criteria emissions for automotive transportation around the world. In this paper, test results for the Gen3X Gasoline Direct Injection Compression Ignition (GDCI) engine are presented. The engine is a 2.2L, four-cylinder, double overhead cam engine with compression ratio ~17. It features a “wetless” combustion system with a high-pressure direct injection fuel system. At low load, exhaust rebreathing and increased intake air temperature were used to promote autoignition and elevate exhaust temperatures to maintain high catalyst conversion efficiency. For medium-to-high loads, a new GDCI-diffusion combustion strategy was combined with advanced single-stage turbocharging to produce excellent low-end torque and power. Time-to-torque (TT) simulations indicated 90% load response in less than 1.5 seconds without a supercharger. For cold starts, the engine is equipped with a fast 2.5kW electric air heater positioned upstream of the intake valves. No spark plugs are used.</div><div class="htmlview paragraph">Dynamometer tests indicated excellent fuel efficiency over the operating map. Minimum BSFC of 194 g/kWh (BTE 43%) was measured at 1750rpm- 12bar IMEP with BSFC less than 210 (40% BTE) over a very wide operating region. The GDCI engine operates on US pump gasoline (RON91) and is ideal for down speeding and uploading for improved vehicle fuel economy. New simulations showed that potentially 48% BTE could be achieved through use of thermal barrier coatings and other improvements to the engine (Gen4X engine).</div><div class="htmlview paragraph">Vehicle simulations were performed at Argonne using the Gen3X engine map for a midsize sedan, SUVs, and a pickup truck. Results indicated a 36 to 51% improvement in combined FTP fuel economy over a competitive 2015 1.6L turbocharged GDi engine equipped with intake variable valve lift. The simulations showed that the Gen3X engine with 12V start/stop or mild hybridization can compete with full hybrid powertrains in various vehicle segments.</div></div>

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