Combustion Improved by Using Flash Boiling Sprays in an Ethanol-Gasoline Optical Engine under Cold Operating Conditions

The development of renewable fuels has attracted widespread attention for internal combustion engines. Among the alternative fuels, ethanol has always been the main substitute for gasoline because it can be readily produced from biomass. However, because ethanol has a higher enthalpy of vaporization than gasoline, it is difficult to evaporate under cold operating conditions. This factor will deteriorate engine output power and exhaust pollutant emissions. To solve this issue, visualization research on the flash boiling combustion process in an ethanol-gasoline optical engine was conducted. This work comprehensively evaluated the spray characteristics, flame propagation behaviors, and exhaust emissions of ethanol-gasoline blends. The fuel temperatures of 30 degrees C, 90 degrees C, and 150 degrees C were used to represent three thermodynamic conditions. The results revealed that the flame propagation speed and flame presence probability index monotonically decrease with a higher ethanol addition under the subcooled injection cases (30 degrees C). However, heating the fuel temperature to 150 degrees C can enhance the evaporation of liquid fuel, which can offset some negative effects from adding ethanol. Thus, consequently, more stable and faster flame formation was achieved by flare flash boiling injection (150 degrees C), which could help promote engine output performance. The net indicated mean effective pressure has been increased from 1.75 to 2.19 bar, an improvement of 25.1%. While the flare flash boiling injection can help reduce PN, THC, and CO emissions, the NOx emission was compromised due to a higher combustion temperature. Finally, this study revealed the flash boiling combustion mechanisms for ethanol-gasoline blends fuels under cold operating conditions.

Automated summary

This study conducted experimental analysis on the injection, flame propagation, and emissions characteristics of ethanol-gasoline blends under different temperature conditions. The results showed that ethanol addition at low temperatures can decrease flame propagation speed, but heating fuel temperature can enhance evaporation and promote more stable and faster flame formation.