Combustion process analysis of methanol/diesel dual fuel engine

In recent years, environment concerns and depletion in petroleum resources have forced researchers to concentrate on exploiting renewable alternatives fuels. As a renewable and alternative fuel, methanol has gained great attendance. As for the application of methanol on compression ignition engines, researchers have focused on partial replacement of diesel with methanol, either blended with diesel or injected into the air intake. Due to the poor miscibility of diesel and methanol, an additive has to be added to form steady methanol/diesel blends. However, majority of these additives have bad influence on NOX emission. Methanol and diesel can also be applied separately to the engine. Dual injection system is one method, which is difficult and expensive to develop. Compared with other methods, intake premixed methanol is more flexible in operation and has greater potential to applied to practical application. In this paper, the methanol injection system was optimally designed according to the former investigation on air-methanol mixture formation inside internal combustion engine. However, previous research results showed that severe knock would happen at high load with high proportion of methanol. In addition, the intake charge temperature declined, owing to the high level of methanol vaporization latent heat. Thirdly, with the addition of methanol, high temperature and low temperature exothermic reaction were delayed, and the ignition delay of dual fuel was prolonged. The premixed methanol injection was controlled by intake manifold electrically system, and the combustion process of methanol/diesel dual fuel was experimentally investigated. Based on the experimental results, the optimization and application of methanol injection system were proposed, and make sure that the output power of optimized dual engine hardly changed. The experimental research was carried out on 4B26 turbocharged diesel engine. The tests were conducted at four different methanol proportion (0, 30%, 40%, and 50%) by changing the methanol injection pulse width. All tests were conducted at two different loads (30%, 80%) at constant engine speed of 2200 rpm. The experimental test results showed that at low load, the peak heat release rate hardly changed, the peak in-cylinder pressure, temperature and ignition delay significantly increased with the increase of premixed methanol proportion. At high load, the in-cylinder pressure, temperature, and peak heat release rate increased, the ignition delay and combustion duration period shortened. At the load of 80% and methanol proportion of 50%, compared with original diesel engine, the premixed burning amount increased, the peak pressure and release rate value of dual fuel increased by 12.1% and 37.7% respectively. It is necessary to optimize the control strategy of methanol/diesel dual engine. According to the influence of dual engine fueled with different methanol proportion on combustion process, the range of methanol proportion was proposed. At the maximum torque speed, the 15%-55% methanol proportion was applicable under different operating condition. High proportion of methanol was available at low load. Nevertheless, with increase of engine load, the methanol proportion has to be strictly controlled. At the load of 80%, because of the limitation of knock, the proportion of methanol should be less than 15%.