Autoignition Characterization of Wet Isopropanol-n-Butanol-Ethanol Blends for ACI 2021-24-0044
In this work, two blends of isopropanol, n-butanol, and ethanol (IBE) that can be produced by metabolically engineered clostridium acetobutylicum are studied experimentally in advanced compression ignition (ACI). This is done to determine whether these fuel blends have the right fuel properties to enable thermally stratified compression ignition, a stratified ACI strategy that using the cooling potential of single stage ignition fuels to control the heat release process. The first microorganism, ATCC824, produces a blend of 34.5% isopropanol, 60.1% n-butanol, and 5.4% ethanol, by mass. The second microorganism, BKM19, produces a blend of 12.3% isopropanol, 54.0% n-butanol, and 33.7% ethanol, by mass. The sensitivity of both IBE blends to intake pressure, intake temperature, and cylinder energy content (fueling rate) is characterized and compared to that of its neat constituents. Both IBE blends behaved similarly with a reactivity level between that of ethanol and n-butanol. The ethanol/isopropanol was able to significantly, though not completely, mute the cool flame reactivity of the n-butanol in the IBE blend. Then, water is blended with both IBE blends to a concentration of 20% water by mass to increase its cooling potential while remaining completely miscible and make it better suited for stratified ACI. The addition of water did not impact the reactivity of the IBE blends. There was a slight combustion efficiency penalty and NOx reduction with water addition. Using a direct injection strategy designed to induce some amount of inhomogeneity to the charge in the cylinder, the high cooling potential of the wet IBE blends increases thermal stratification, elongating the combustion process and reducing energy release rates. This enables high load ACI using renewable alcohol fuels with only a slight combustion efficiency penalty that is attributed to elongating the combustion process enough to protect the engine.
