Study On Fuel Reforming Of RM-HCCI Combustion

The shortage of energy and the deterioration of environment put forward further requirements for the development of high efficient combustion technologies in internal combustion engines. Many advanced combustion strategies have been introduced in the past decades such as HCCI, LTC and so on. Most of these studies are based on the first-law analysis, which can only provide limited information about the potential of a system to produce useful mechanical work. In fact, the combustion processes are irreversible actions that would loss approximately 20-25% of the fuel's working potential in conventional combustion conditions. Understanding the mechanism of the inefficiencies and seeking for ways to reduce the irreversibility are significant to realize further improvement of the engine efficiency, thus the second law analysis is needed.According to the characteristics of the available energy loss distribution in the combustion process, a new type of fuel reforming system based on the RM - HCCI (Reformed Molecule-Homogeneous Charge Compression Ignition) combustion principle have been designed. In which, the direct pyrolysis of larger molecule fuel of n-heptane recovering part of engine exhaust energy transforms the fuel into small molecules before being injected into the cylinder, in this way we can reduce the exergy loss in the combustion process and improve the thermal efficiency. The effects of the reforming boundary conditions such as temperature, oxygen concentration, pressure on reforming molecular selectivity and chemical exergy distribution are studied with detailed chemical reaction mechanism of n-heptane. The advantages of fuel reforming are evaluated through combining chemical kinetics with thermodynamic equilibrium algorithm. Results have shown that fuel reforming can effectively reduce the exergy loss of combustion process and improve the second law thermal efficiency when fuel is reformed under the high temperature and low oxygen reforming conditions.In order to verify the feasibility of RM-HCCI fuel reforming theory, a reforming flow reactor test bench system comprises of the carrier gas supply system, fuel supply system, controllable heating system, mixed reactor assembly and data analysis system was designed according to the RM-HCCI fuel reforming principle. The experimental results being agreed well with the simulation results verified the feasibility of the RM-HCCI fuel reforming theory and the controllability of reforming boundary.Taking the Reforming environment of the test bench as a reference, the reforming process proceeds is analyzed under medium load of the engine by applying the second law analysis, results show that chemical exergy of the reformed fuels can be improved over 3.5% through optimizing the reforming conditions.