Abstract
Alcohol fuels are potential alternative fuels for low-temperature combustion concepts in internal combustion engine applications. In this work, 80 vol% of ethanol and 80 vol% of n-butanol are blended with 20 vol% of n-heptane, respectively. These two alcohol fuel blends are investigated in a combustion research unit and a single-cylinder heavy-duty engine to compare the combustion and emission characteristics. The effects of EGR rate and achievable operating load range when using ethanol and n-butanol are the major goals of this investigation. The results show that the ethanol fuel blend requires much higher temperatures to auto-ignite than do the n-butanol blend and diesel. Both alcohol fuel blends show negligible soot emissions in the medium load range when operated with a 40% EGR rate. However, the ethanol fuel blend produces more nucleation mode particles and fewer accumulation mode particles compared to the n-butanol fuel blend under the same operating condition. Furthermore, the particulate size distribution shows that diesel generates more particles with larger particle diameters and thus more soot mass compared to alcohol fuel blends. Still, both alcohol fuel blends can be operated from low to high load with simultaneous reduction of NOx and soot emissions but at the cost of increased HC and CO emissions. The Euro VI-regulated soot mass and particle number are achieved from low to medium-high load for alcohol fuels. Diesel has the great advantage of achieving high combustion efficiency but shows a NOx/soot tradeoff at a high EGR rate. Generally, the ethanol fuel blend yields the lowest gross indicated efficiency in the whole test range compared to diesel and the n-butanol fuel blend due to the necessity of inlet heating, which decreases the thermal efficiency. The n-butanol fuel blend achieves the highest gross indicated efficiency (above 50%) in the medium-high load range.
Highlights
The awareness of global warming and greenhouse gas (GHG) emissions gives rise to widespread attention on CO2 reduction
Vehicles running on alcohol fuel blends produce less net CO2 than conventional fossil fuel vehicles per mile traveled (Wang et al, 2012)
The ignition delay period consists of both the physical delay, wherein liquid fuel breaks up into small droplets, atomizes, vaporizes, and entrains ambient air, and the chemical delay contributed by pre-combustion reactions
Summary
The awareness of global warming and greenhouse gas (GHG) emissions gives rise to widespread attention on CO2 reduction. The agreed-upon targets for light commercial vehicles, aim to reduce the average CO2 emissions by 15% in 2025 and Alcohol Fuel Application in LTC by 31% in 2030. Among the renewable energy sources, alcohol fuels are often labeled “green” from a life cycle point of view. The CO2 released from alcohol fuels when used in vehicles can be offset by the CO2 captured by the crops that are used to produce alcohol fuels. Vehicles running on alcohol fuel blends produce less net CO2 than conventional fossil fuel vehicles per mile traveled (Wang et al, 2012). Bio-alcohol fuels can achieve CO2 reduction potential ranges from 35 to 80% depending on the biomass and process technology used (Schwaderlapp et al, 2012)
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