Researchers from the University of Illinois and colleagues in China investigating the performance, combustion and emission characteristics of a port fuel-injection SI engine fueled with isopropanol-n-butanol-ethanol (IBE)-gasoline blends have concluded that an IBE30 blend could be a good alternative to gasoline.
Bio-n-butanol itself is a promising alternative fuel, produced conventionally from the fermentation of carbohydrates by Clostridium bacteria in a well-established process referred to as ABE fermentation, after its major chemical products: acetone, butanol and ethanol. However, ABE fermentation production suffers from relatively low production efficiency as well as the high cost of component recovery; the product mixture typically has an A:B:E ratio of 3:6:1.
To reduce the impact of the cost issue, other studies have explored the use of the full ABE mixture as a fuel; ABE-diesel blends showed potential to increase thermal efficiency and decrease soot emission. However, the acetone in ABE is potentially corrosive to the engine parts composed of rubber or plastic.
However, some natural Clostridium beijerinckii strains produce isopropanol instead of acetone, together with butanol and ethanol (IBE) to produce an alcohol mixture.
… isopropanol shows a higher energy density than acetone (23.9MJ/L vs 22.6 MJ/L). It also has been reported that isopropanol can be used as a fuel additive for the preparation of high-octane gasoline. Therefore, the objective of this study is to evaluate the use of IBE-gasoline blends in a port fuel-injected SI engine based on the investigation on performance, combustion and emissions characteristics.—Li et al.
For the study, the team compared IBE-gasoline blends with various IBE content (0–60 vol.% referred to as G100-IBE60) and more commonly used alternative alcohol fuels (ethanol, n-butanol and ABE)-gasoline blends.
Pure commercial summer gasoline with research octane number (RON) of 92 was the baseline fuel. The team mixed acetone, n-butanol, isopropanol and ethanol to provide ABE and IBE mixtures with a volume ratio of 3:6:1 (A:B:E or I:B:E). This ratio was used to simulate the composition of the ABE and IBE fermentation product.
The test engine was a single-cylinder SI engine with identical cylinder geometry to a 2000 Ford Mustang Cobra V8 (575 cm3 displacement, 9.6:1 compression ratio).
Engine speed was fixed at 1200 rpm. The throttle plate was fully opened and the intake manifold pressure was fixed at 60 kPa and 90 kPa by regulating the compressed air, which corresponded to engine loads of 300 kPa BMEP (Brake Mean Effective Pressure) and 500 kPa BMEP. The engine was running at the spark timing corresponding to gasoline’s MBT at stoichiometric condition. Equivalence ratio varied over a range of lean and stoichiometric conditions, i.e. Φ varying from 0.83 to 1.
They found that combustion phasing was advanced with increasing IBE content. The negative effect of improper combustion phasing was offset by improved combustion quality as a result of fuel-borne oxygen and reduced combustion duration.
Broadly, they found that IBE30 performed well with respect to engine performance and emissions, including brake thermal efficiency (BTE); brake specific fuel consumption (BSFC); carbon monoxide (CO); unburned hydrocarbons (UHC); and nitrogen oxides (NOx).
IBE30 showed a similar BTE relative to that of G100 and 1.0% and 1.4% higher BTE than that of IBE10 and IBE60, respectively. For the emissions, IBE30 provided better results based on its lower CO (4.2%), UHC (18.9%) and NOx (5.5%) emissions than those of G100.
They then compared IBE30 with some commonly used alternative alcohol fuels, including E30, B30 and ABE30. E30 and B30 had a more advanced combustion phasing, which also caused the relatively lower BTE than that of ABE30 and IBE30. A significant increase of CO and UHC emissions occurred with E30 and ABE30, respectively. Similar NOx emissions were produced by the different fuels.
The researchers also compared IBE30 with G100 under various equivalence ratio (Φ = 0.83–1) and engine load (300 and 500 kPa BMEP).
Overall, they found higher BTE (0.04–4.3%) and lower CO (4%), UHC (15.1–20.3%) and NOx (3.3–18.6%) emissions were produced by IBE30 compared to G100.
IBE could be a good alternative to gasoline based on the fact that it can be produced using an environmentally benign fermentation process (from non-edible biomass feedstock and without recovery process) and has the potential for improving energy efficiency and reducing pollutant emissions.—Li et al.
Yuqiang Li, Lei Meng, Karthik Nithyanandan, Timothy H. Lee, Yilu Lin, Chia-fon F. Lee, Shengming Liao (2016) “Combustion, performance and emissions characteristics of a spark-ignition engine fueled with isopropanol-n-butanol-ethanol and gasoline blends,” Fuel, Volume 184, Pages 864-872 doi: 10.1016/j.fuel.2016.07.063