Study Finds Strong Synergy Between Spark Ignition Engine Downsizing and Low-to-Moderate Alcohol Blend Fuels
A study by engineers from Mahle Powertrain Ltd and BP found strong synergy between spark ignition (SI) engine downsizing and fuel containing low-to-moderate amounts of alcohol, including ethanol and butanol. The team presented a paper on their work at the recent SAE 2009 World Congress in Detroit.
The researchers found that the combination of technologies allowed improvements in fuel economy over the engine drive cycle. Furthermore, a reasonable improvement in dilution tolerance could be achieved at higher engine loads, which could eliminate over-fueling requirements under such conditions.
Among their findings was that for gasoline fuels, aggressively downsizing the engine and adopting homogeneous direct fuel injection enabled an improvement in fuel consumption of ~17% over the New European Drive Cycle compared to a naturally aspirated PFI unit.
When alcohol was added to the blend, fuel consumption over the drive cycle increased in direct proportion to the reduction in calorific value of the fuel. For example, with E85, the calorific value was 32% lower than the 98 RON fuel while the fuel consumption was 33% higher.
Small improvements in thermal efficiency when using E85 under part-load drive cycle conditions are vastly outweighed by the deficit in the calorific value of this fuel.—Cairns et al. (SAE 2009-01-0138)
The team studied three variants of gasoline (95, 98 and 102 RON) , three gasoline-ethanol blends (E10, E22 and E85), and a gasoline-butanol blend (Bu16) covering a range of oxygen concentrations and octane numbers.
|Key Properties of the Test Fuels|
|Property||95 RON||98 RON||102 RON||Bu16||E10||E22||E85|
|Lower Heating Value (MJ/kg)||43.16||43.06||42.34||41.88||41.64||39.96||29.28|
|Density @ 15 °C (kg/m3)||0.74||0.75||0.74||0.75||0.75||0.75||0.78|
|O2 (% wt)||0||0||2||3.35||3.35||6.8||29.5|
Combustion of the fuels was evaluated in a turbocharged four-cylinder 2.0-liter four-valve per cylinder direct fuel injection research engine equipped with a standard three-way catalyst (TWC) and an external EGR circuit that allowed use of either cooled or non-cooled EGR.
The team studied fuel injection timing and pressure; excess air tolerance; EGR tolerance; and spark retard limits at both part and boosted high load conditions. They determined relative in-vehicle fuel economies via drive cycle simulation for comparison to a naturally aspirated (NA) gasoline port fuel injection (PFI) engine.
Among the other conclusions for operation under part load conditions were:
Alochol blends generally performed better when injected at slightly later timings and marginally lower fuel pressures.
E22 produced the highest smoke readings with early injection timing; E85 produced negligible smoke in this engine, even at late injection timings and low fuel rail pressures.
Blends with lower alcohol content allowed small improvements in EGR tolerance; only E85 showed a notable increase in tolerance.
The addition of alcohol did not improve excess air tolerance.
E10 and Bu16 produced similar fuel consumption values under the conditions tested.
Future work shall be concerned with the combustion, performance and emissions of alcohol fuels across the speed-load map of an aggressively downsized, state-of-the-art, twin-turbocharged three cylinder SI engine.—Cairns et al. (SAE 2009-01-0138)
Alasdair Cairns, Neil Fraser, Hugh Blaxill, Martin Gold, John Rogerson, Craig Goodfellow. A Study of Gasoline-Alcohol Blended Fuels in an Advanced Turbocharged DISI Engine. (SAE 2009-01-0138)