LTC performance of C1–C4 water-alcohol blends with the same cooling potential

Abstract

Alcohols are renewable fuels with high cooling potentials and low φ-sensitivity, ideal properties for highly controllable low temperature combustion (LTC) concepts that enable high-efficiency, low-emissions operation. Recent work showed that the C1–C4 alcohols behave similarly in LTC. The primary difference between these fuels is their cooling potential, which impacts their stratified LTC behavior. To homogenize the stratified LTC performance of these fuels and create an equivalence class of fuels, water can be blended with these fuels to increase their cooling potential to some benchmark value. When ethanol or propanol is blended with water to WE80 (80% ethanol, 20% water) or WP70, no significant change in the sensitivity of the fuel to operating conditions occurs, with a 1–2 percentage point decrease in combustion efficiency and a slight decrease in NOx occurring with WP70. The isomers of butanol are not fully miscible with water and require a C1–C3 alcohol as a co-solvent. W25E50B25 (25% water, 50% ethanol, and 25% of one of the three butanol isomers (n-, iso, or sec-)) behaved similarly to WE80. The ethanol in the blend was able to mute the cool flame reactivity of n-butanol and sec-butanol, further homogenizing the LTC performance of these fuels. Overall, when ethanol, propanol, or butanol are blended with water to have the same cooling potential as methanol, there is no appreciable difference in their LTC performance (demonstrating interchangeability) other than a small combustion efficiency penalty, particularly at low loads. When load increases or when combustion is advanced, this penalty decreases.