Rapid compression machine studies on ignition delay change of PRF HCCI combustion by using chemical additives

Engines with high efficiency and low emissions are getting more and more attention, due to the growing concerns regarding the lack of fossil fuels and air pollution. The HCCI(Homogeneous Charge Compression Ignition) engine is one of most promising types of future engines, as it has high efficiency and low emissions. This is attributed to its high compression ratio and low temperature combustion(LTC), respectively. However, the HCCI engine has two main problems. First, the combustion phasing is too difficult in the HCCI engine. That's because the HCCI engine doesn't have an ignition controlling device, such as a spark plug in the SI(Spark Ignition) engine and a fuel injector in the CI(Compression Ignition) engine, so the intrinsic chemical characteristic of the fuel determines the combustion phase of the HCCI combustion. Second, the HCCI engine can't operate stably at high load because of the high risk of knocking. This is why the current automobile engines are driven at HCCI mode in moderate conditions, but they are changed to conventional modes at high load. To solve the difficulty of the combustion phasing in the HCCI engine, it is important to find the way to control ignition delay without a spark plug or a fuel injector. The main purpose of this study is to assess the feasibility to control the ignition delay of the PRF(Primary Reference Fuel) HCCI combustion using chemical additives such as DTBP(Di-tert-butyl peroxide) and hydrogen. The amount of DTBP was calculated on a molar basis, and the amount of hydrogen was calculated on a HHV(Higher Heating Value) basis. PRF0, PRF50, PRF100 were used as fuel. RCM(Rapid Compression Machine) was used to represent the HCCI combustion, and premixed homogeneous charge was prepared in the fuel mixer with the magnetic stirrer. When DTBP was added, the ignition delay was decreased greatly even when the amount of DTBP was 0.1% of the fuel. In contrast, the ignition delay increased when hydrogen was added. Result of PRF50 experiments is shown in the figure 1, for example.