Investigation on spray and soot lift-off length of an ABE-diesel blend in a constant volume chamber with diesel engine conditions

Acetone-Butanol-Ethanol (ABE), an intermediate product in the ABE fermentation process for producing bio-butanol, is considered as a promising alternative fuel because it not only preserves the advantages of oxygenated fuel, which typically emit less pollutants compared to conventional diesel, but also lowers the cost of fuel recovery for each individual component during the fermentation. In this work, 20% ABE with component ratio of 3:6:1 and 80% ultra-sulfur diesel by volume, referred as ABE20, and pure diesel, referred as D100, were injected and combusted in a constant volume chamber with the ability to mimic high temperature and high pressure conditions of real diesel cylinder near the top dead center. By adjusting intake partial pressure and injection timing, the ambient oxygen concentration and temperature for fuel injection can be controlled. Ambient temperatures were set at 1100K, 900K and 700K to cover conventional temperature combustion and low temperature combustion, while the ambient oxygen concentrations were set at 21%, 16% and 11% to cover different EGR ratios separately. Spray and natural flame images were captured by a high speed camera coupled with a copper vapor laser as a light source. The results show that spray liquid penetration and soot liftoff length are shorter and much longer for ABE20 than those for D100 separately under all tested conditions, which form a much bigger gap from spray tip to the combustion area for ABE20. A big gap reduces the local equivalence ratio at the combustion area and then suppresses the soot formation due to the gap is the most effective area for air-fuel mixing processes. Indeed, the natural flame luminosity which represents the soot emission level of ABE20 is significantly lower than that of D100 at all tested conditions. At the same time, ABE20 performed a similar combustion phasing with D100 under high ambient temperature, but experienced an aggressive retardation under low ambient temperatures especially with low ambient oxygen concentrations. In addition, ABE20 did not show a stronger concentrated premixed combustion since its heat release rate peak is lower than that of D100, which was also confirmed by its longer combustion duration. Therefore, ABE20 expresses a high potential to reduce soot emissions but it also has to face combustion deterioration at low temperature combustion conditions.