Ignition and Combustion Controls of Synthetic Fuel using Diesel Engine with Variable Valve Timing System [First Report]

Because the transportation industry uses fossil fuels as much as 1/4 of the total, CO2 emission from transport sector should be reduced. Therefore, carbon neutral (CN) fuel has been attracted attention. However, hydrogen and ammonia have low energy density and are difficult to be stored and transported. In this study, synfuel produced by Fischer-Tropsch (FT) reaction. This fuel is produced with carbon dioxide absorbed from the direct air capture and electricity derived from renewable energy, so it is possible to achieve CN. However, FT fuel tends to have less aromatics and a higher cetane number than diesel fuel. Therefore, excessive early ignition occurs at low speed and low load in application to diesel engine. The purpose of this study is to suppress early ignition by controlling the amount of air flowing into the cylinder. The numerical results showed that the ignition timing and combustion could be controlled using Miller cycle by late intake valve closing (LIVC). In addition, by controlling the ignition timing with LIVC, it became possible to prolong the ignition delay period, and premixed charge compression ignition (PCCI) combustion was realized in the low-speed low-load region. This combustion improved indicated mean effective pressure with high degree of constant volume. Additionally, decrease in fuel-rich zones derived from long ignition delay period reduced NOx and soot emissions. From the above, the possibility of improving combustion and exhaust emission performances by applying the Miller cycle using LIVC when using FT fuel was demonstrated.