The absorptivity of multilayer micro-perforated panel absorber(MPA) usually is estimated by the equivalent circuit(EC).Recently,there are attempts to use the impedance transfer method(ITM) or the transfer matrix method(TMM) to calculate the absorptivity.It is necessary to compare the three methods.The corresponding experiments are carried out for the comparison.Theoretical analysis and experimental results show that the ITM and TMM are the essentially same,and their calculation results are consistent with the experimental data.However,the calculations results using EC disagree with experimental data,especially for the structure with long cavity.EC is a kind of concentrated parameter analysis method.For a multilayer structure,this method only considers acoustic compliance,while ignores the effect of acoustic mass.Thus,it will cause calculation error.This kind of error does not exist in ITM and TMM,thus they are more accurate than EC.

The micro-emulsion fuels were prepared with complex surfactant, and the effects of temperature on the stability of these fuels were investigated. The engine performance and the emissions were studied when the engine was fueled with diesel and micro-emulsion diesel respectively. Results showed that when the engine was fueled with micro-emulsion diesel, the NOXand smoke emissions were decreased obviously and HC and CO emissions were increased slightly. Discounting of surfactant and water, the specific fuel consumption of micro-emulsion diesel was lower than those of diesel under any load at the speed of 2900r/min.

Because of the crisis of energy resource, the rising price of energy and the stringent emission law , it is necessary to look for alternative fuels which are renewable and environmental friendship . Microemusified bio-diesel which can be stored for long periods is one of these alternative fuels. Three kinds of new microemulsions containing different percentages of bio-diesel, water and surfactant (OP4-OP7) were prepared , and the influence of the temperature to stability was discussed. The performance and emissions of a diesel engine running with the microemlsion were investigated. The result showed that the temperature have great effect on the stability ,the higher the temperature ,the worse the stability , and the diesel engine with the biodiesel microemulsions can run normally and the NOx and smoke emission are reduced greatly.

The microemulsified biodiesel is a kind of prospective alternative fuel,whose advantages are reductions in the emissions of nitrogen oxides and particulate matters and good economical performance.Take TX4 and TX7 surfactants as compound emulsifying agent.The effects of KHLB value and proportion of mixed surfactants,emulsified method,water quality,the type of alcohol and the ambient temperature on the stability of microemulsion were studied systematically.The results show that the appropriate proportion of compound emulsifying agent is helpful to form the microemulsion,but the emulsified method,the water quality and the type of alcohol have little influence on forming the microemulsion.It is also found in the research that the temperature has a great effect on the stability of microemulsion,that is to say,the stability will be worse if the temperature is high.