Ogawa, H., Shibata, G., Jin, X., Hirose, T. et al., "Visualization and Heat Release Analysis of Premixed Diesel Combustion with Various Fuel Ignitabilities and Oxygen Concentrations in a Constant Volume Combustion Vessel," SAE Technical Paper 2013-01-0899, 2013, https://doi.org/10.4271/2013-01-0899.
Low NOx and soot free premixed diesel combustion can be realized by increasing ignition delays in low oxygen atmospheres, as well as the combustion here also depends on fuel ignitability. In this report single intermittent spray combustion with primary reference fuels and a normal heptane-toluene blend fuel under several oxygen concentrations in a constant volume combustion vessel was analyzed with high-speed color video and pressure data. Temperature and KL factor distributions are displayed with a 2-D two-color method.The results show that premixing is promoted with a decrease in oxygen concentration, and the local high temperature regions, above 2200 K, as well as the duration of their appearance decreases with the oxygen concentration. With normal heptane, mild premixed diesel combustion can be realized at 15 vol% oxygen and there is little luminous flame. However, at 18 vol% oxygen, premixing and lowering of the temperature were inadequate to decrease the total value of the KL factor, showing that soot formation was not avoided.The premixing is also promoted and the local high temperature regions decrease with lower fuel ignitabilities, and with lower fuel ignitabilities the total KL factor decreases. However, the combustion with lower fuel ignitabilities at 21 vol% oxygen is more rapid than at lower oxygen concentrations.The ignition delays with normal heptane - toluene blends are larger than with primary reference fuels with the same research octane numbers, showing the lower ignitability of toluene. However, the flame luminosity, total KL factor, and high temperature flame regions with the toluene blend are larger than with the primary reference fuel.