Investigation Of Spray Characteristics And Combustion Process For A Biodiesel Fueled Direct Injection Rotary Engine

With the aggravation of energy crisis and environmental pollution,people urgently need more clean and efficient new power plant,which makes burning of fuel in the traditional engine face more and more serious problems.In this context,finding new alternative fuels and improving engine combustion efficiency are the two best ways to deal with these challenges.For the first way,biodiesel which is a clean fuel,has a power capacity that is comparable with the conventional diesel fuel and can also effectively reduce engine emissions making it one of the ideal alternative fuels for diesel engines.Secondly,researchers are trying to improve the efficiency of the traditional reciprocating engines,as well as raising new types of engines.As a new type of internal combustion engine,the rotary engine essentially has the advantages of light mass,high work-weight ratio and smooth operation.It is one of the replacementsto the traditional reciprocating engines.In conclusion,the rotary engine fueled with biodiesel can combine the advantages of both biodiesel and rotary engine,and is a new high efficiency power plant with bright future.However,the special structure and operation of rotary engine is different from the reciprocating engine,so the mixing process and combustion process are different in the cylinder.The narrow combustor will make the flame easily quenched and a lot of unburned hydrocarbon remains during the propagation process.When biodiesel is used,the slower atomization evaporation rate of biodiesel will further aggravate the problem,and the basic research of the working process of the biodiesel fueled rotary engine is far from enough at present.Therefore,it is of great scientific significance and practical value to conduct basic researches on airflow movement,spray characteristics and combustion process of biodiesel fueled rotary engine,as well as optimize the structure and technical parameters of biodiesel fueled rotary engine.In this paper,taking the biodiesel fueled rotary engine as the research object,the formation law of the mixture in the cylinder and the flame propagation mechanism are regarded as scientific problems.A biodiesel spray test bed was set up to test and analyze the basic spray characteristics of biodiesel under rotary engine conditions.At the same time,on the basis of CFD software,the dynamic grid movement is realized by programming,and the corresponding turbulence model,combustion model,ignition model and simplified chemical reaction mechanism comprising thenumerical models were validated against experimental results.The threedimensional flow field,temperature field and the concentration of some intermediate products in the cylinder under the condition of common rotational speed which is not easy to obtain by experiment are calculated.On this basis,the effects of fuel injection timing,advance spark timing and application of different equivalence ratios on the mixture formation and combustion process of biodiesel fueled rotary engine were studied systematically.The research results with academic significance and practical value are as follows:1.The basic characteristics of biodiesel spray in a constant volume vessel under rotary engine operating conditions were studied.The results show that both reasonable spray penetrations distance as well as spray cone angle expansion is a key factor to improve the fuel-air mixture.This condition was attained at 550 K 2.0MPa with the penetration length not exceeding 60 mm.The spray penetration distance decreases and the spray cone angle expand as the ambient back pressure increases,which is beneficial to improve the fuel atomization quality.2.A three-dimensional dynamic simulation model of the biodiesel fueled rotary engine was established and reasonable turbulence model,spray model,ignition and combustion model were added,and combining with the skeletal oxidation biodiesel chemical reaction mechanism was used to carry out numerical simulation work on the mixture formation and combustion reaction process in-cylinder.Combined with experimental data the simulation model was validated to make it reliable.Furthermore,mixture formation and biodiesel fuel distribution in the cylinder during the working process of the DIRE at the experimental conditions were obtained by means of simulations.3.The effect of in-cylinder mixture formation at fuel injection time was calculated on the established three-dimensional numerical simulation model.The results show that the distribution of fuel in the cylinder is smaller with late injection time,that is,the more uneven distribution of fuel and vice versa at early injection time.However,at 80°CA BTDC liquid phase evaporation of biodiesel fuel mass fraction was conducive to rotary engine performance improvement.Critical information difficult acquiring through experiment such as the flow field,temperature field and some intermediate concentration fields in the combustion chamber were also obtained.4.The effect of advance ignition time on combustion process in-cylinder was calculated on the established three-dimensional numerical simulation model.The results show that the proper advance of ignition time,in this case 35°CA BTDC,is beneficial to fully utilize the acceleration of flame propagation by in-cylinder eddy current,thus improving the combustion efficiency of engine.5.High burning rate is achieved when biodiesel fuel is concentrated at the middle position of combustion chamber and between the trailing spark plug and leading spark plug.In this instance when the fuel is located at 30mm(X-axis)and 15mm(Z-axis)from the centerline in opposing directions.This can make full use of the sparks ignition effect to combust the fuel in the combustion chamber as it is conducive to the ignition and unique flame propagation process(back to front)of RE that leads to balanced combustion.6.The effect of different equivalence ratios on combustion process in-cylinder was calculated on the established three-dimensional numerical simulation model.The results show that the distribution of fuel in-cylinder is less concentrated at lean condition and more concentrated at rich condition during start of ignition.The results also show that lean condition is beneficial to the reduction of emissions and fuel economy at the expense of output power.However appropriate lean condition,in this case 0.8 equivalence ratio,is beneficial to the reduction of emissions,fuel economy as well as reasonable output power thus improving the combustion efficiency of engine.This paper provides the experimental and simulation basis for the research of biodiesel fueled rotary engine and provides theoretical guidance for improving its combustion efficiency.Meanwhile,the research methods and conclusions presented in this paper are useful for the development of other fuel rotary engine systems.