Spray, Ignition, and Combustion Characteristics of Diesel, Propanol, and Pentanol Blends in a Constant Volume Chamber

Bioalcohols are considered a popular alternative to traditional fuels due to their renewability and their potential of emissions reduction. In order to further investigate the effects of the fuel properties and the ambient conditions on the combustion process, the spray, ignition, and combustion characteristics of diesel, propanol, and pentanol blends were evaluated in a constant volume chamber. Pure diesel was used as the baseline fuel; propanol (Pr) and pentanol (Pe) were mixed with diesel by 20% (v/v) as test fuels. The ambient temperature was varied from 800 to 1200 K and the ambient density was varied from 11 to 15 kg/m3, which covers the in-cylinder conditions for diesel engines at top dead center when operating at both sea level and high altitudes. The spray evolution was measured using Mie scattering methods, and the combustion process was directly recorded using a high-speed camera. The results showed that a lower ambient temperature or density could prolong the liquid penetration length, ignition delay, and the flame lift-off length (FLoL). The combustion duration and natural flame luminosity would decrease when lowering the ambient temperature or elevating the ambient density. However, all these characteristics for the test fuels are more sensitive to the ambient temperature compared to the ambient density. The fuel type also plays an important role. At low (800 K) and medium (1000 K) ambient temperatures, the penetration length of Pe20 was slightly shorter than that of diesel, while that of Pr20 was a little longer compared to diesel. Pr20 and Pe20 experienced longer ignition delays than diesel at a low (800 K) ambient temperature. At a high ambient temperature (1200 K), Pr20 showed the shortest ignition delay, and Pe20 had a similar or shorter ignition delay compared to diesel. Pr20 showed the shortest combustion duration among the test fuels under all ambient conditions followed by Pe20; diesel experienced the longest combustion duration. At a low temperature of 800 K, the addition of alcohols can significantly prolong FLoL and adding propanol resulted in a longer FLoL. Both Pr20 and Pe20 showed smaller time-integrated natural luminosity values due to the longer FLoL of fuel blends, fuel-bonded oxygen, and the replacing effect of alcohol. This illustrates that the addition of alcohol can help to inhibit the formation of soot.