Experimental Investigation of Spark-Ignited Combustion with High-Octane Biofuels and EGR. 1. Engine Load Range and Downsize Downspeed Opportunity

Abstract

The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form and in midlevel alcohol−gasoline blends with 24% vol/vol isobutanol−gasoline (IB24) and 30% vol/vol ethanol−gasoline (E30). A single-cylinder research engine was used with an 11.85:1 compression ratio, hydraulically actuated valves, laboratory intake air, and was capable of external exhaust gas recirculation (EGR). Experiments were conducted with all fuels to full-load conditions with λ = 1, using both 0% and 15% external cooled EGR. Higher octane number biofuel blends exhibited increased stoichiometric torque capability at this compression ratio, where the unique properties of ethanol enabled a doubling of the stoichiometric torque capability with E30 as compared to 87 AKI, up to 20 bar IMEPg (indicated mean effective pressure gross) at λ = 1. EGR provided thermodynamic advantages and was a key enabler for increasing engine efficiency for all fuel types. However, with E30, EGR was less useful for knock mitigation than gasoline or IB24. Torque densities with E30 with 15% EGR at λ = 1 operation were similar or better than a modern EURO IV calibration turbo-diesel engine. The results of the present study suggest that it could be possible to implement a 40% downsize + downspeed configuration (1.2 L engine) into a representative midsize sedan. For example, for a midsize sedan at a 65 miles/h cruise, an estimated fuel consumption of 43.9 miles per gallon (MPG) (engine out 102 g-CO 2 /km) could be achieved with similar reserve power to a 2.0 L engine with 87AKI (38.6 MPG, engine out 135 g-CO 2 /km). Data suggest that, with midlevel alcohol−gasoline blends, engine and vehicle optimization can offset the reduced fuel energy content of alcohol−gasoline blends and likely reduce vehicle fuel consumption and tailpipe CO 2 emissions. ■ INTRODUCTIONThe Energy Independence and Security Act 1 of 2007 requires that, by year 2022, 36 billion gallons per year of bioderived fuels need to be consumed in transportation. This uptake in bioderived fuels is a more than a 7-fold increase from the 4.7 billion gallons consumed per year when the law was enacted. The rules for complying with this mandate are specified by the U.S. Environmental Protection Agency (EPA) in the Renewable Fuel Standard II (RFS II). 2 When the total transportation energy consumption is analyzed, it is apparent that this legislation increases the usage of biofuels. In 2012 the United States consumed 27.97 quadrillion BTU of energy for transportation, and it is projected to consume 29.24 quadrillion BTU in 2022. 3 Assuming gasoline equivalent energy of 42.8 MJ/kg and density of 740 kg/m, 3 the RFS standard will require an increase in the percentage of transportation energy from biofuels to approximately 14% in 2022 from the approximate 2% in 2007. To date, the RFS II progress has seen more than a doubling of biofuel usage, with the annual recorded share of transportation energy from nonpetroleum sources totaling 4.3% in 2012. Although 2012 was the year wi...

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

“…Ethanol, the most commonly used renewable fuel, has a research octane number (RON) of approximately 110 [6] compared to typical U.S. regular gasoline at 91-93 [2]. Accordingly, high octane number ethanol blends containing from 20 volume percent (vol%) to 40 vol% ethanol are being extensively studied [3,7,8,9,10]. A unique property of ethanol is its high heat of vaporization (HOV), which significantly increases charge cooling for DI engines, providing additional knock resistance.The tendency of a spark-ignited engine fuel to autoignite and cause knock is measured as the octane number, a critical performance parameter for SI engines.…”

An assessment of thermodynamic merits for current and potential future engine operating strategies

“…In other words, the pressure trace can be found for any arbitrarily prescribed heat release and composition profile. For this work, we have chosen to represent the heat release rate with a normal distribution, shown in equation (7), as it requires the specification of only two parameters (mean, m, and standard deviation, s), is symmetric about its mean, and is equivalent to the Otto cycle in the limiting case that m = 0 CA degrees (°CA) after top dead center (aTDC) and s = 0 8 CA. An experimental condition can be modeled simply by setting m equal to the combustion phasing as represented by the crank angle at 50% of heat release (CA50) and by setting s such that the combustion duration, or number of crank angles between 25% and 75% of heat release (CA25-75), of the resulting normal distribution will match that of the heat release ðCA25 À 75 ffi 1:35sÞ.…”

“…3,4 At high loads, SI engines are limited by knock, and this is exacerbated by the downsizing trend. Methods of raising the knock limit include reducing compression ratio (r c ) 5 which reduces efficiency, increasing fuel AKI, [6][7][8] and the use of exhaust gas recirculation (EGR), which can result in efficiency gains comparable to compression ratio increases, 9 and also introduce problems with combustion stability. 10,11 CI engines operating with a CDC strategy rely on combustion that is mixing-controlled, where combustion control is achieved through injection timing and pressure.…”

Petroleum refinery greenhouse gas emission variations related to higher ethanol blends at different gasoline octane rating and pool volume levels

“…Higher levels of renewable fuel with current engine technologies could reduce GHG emissions. However, another more intriguing approach, deemed publicly by major US automakers to be a promising pathway for compliance with both increasing renewable fuel volume requirements under the RFS and progressively more stringent corporate average fuel economy (CAFE) requirements, is a transition to advanced engine technologies with greater use of ethanol to reduce GHG emissions . This approach involves using higher engine compression ratios (CR), direct injection, and potentially turbocharging in order to improve thermal efficiency and reduce engine weight without power loss, which translates into lower tailpipe GHG emissions and less fuel consumption per mile.…”

“…Taking advantage of ethanol's higher octane rating and charge cooling effect, engine designs can be optimized to offset ethanol's reduced energy content, thereby reducing vehicle fuel consumption and tailpipe CO 2 emissions relative to current engine designs. Splitter and Szybist concluded CO 2 reductions could be achieved without a decrease in miles per gallon with an intermediate ethanol blend providing reduced knock and tolerating a higher CR. Anderson et al .…”