Fundamental Research On Combustion Issues Of Natural Gas Internal Combustion Engine

Natural gas is considered to be an ideal alternative fuel for internal combustionengine. Still some problems in natural gas internal combustion engine, such as thecombustion heat release, the cyclic combustion variations and the fuel combustioncharacteristics, have not already totally solved yet. By necessary means, basicresearching on the combustion issues of natural gas engine has a high theoreticalvalue for enhancing the engine performance. In this paper, experimental study oncombustion characteristic parameters of natural gas engine and combustionsimulation to methane (primary component of natural gas) and its mixture are used.Firstly of all, combustion experiments were carried out in a natural gas engine.Basing on calculating software LabVIEW, three kind of heat release modelincluding G model, R model and A model were compiled. Effect of operatingparameters to the heat release models‘calculation results of natural gas engine wasstudied to confirm the models‘application conditions. The calculated results showthat, the results calculated differences between A and R models is not obvious,therefore, both of them can be in common use. The three models are affectedslightly by ignition advance angle and excess air ratio. The calculation results ofGatowski et al. model are affected significantly by engine speed. The three modelssubstitutes mutually under the condition of small throttle opening or high enginespeed.Afterwards, the coefficient of variations of IMEP (COVIMEP) were compiled intocalculating formulas, by which, the thermodynamic parameter were calculated usingcylinder pressure.The influence of ignition timing on COVIMEPwas investigated. Putforward a concept of minimum COVIMEP(MCV) ignition timing, and then comparedthe results of influences of different factors on cyclic combustion variations by usingfixed ignition timing and minimum MCV ignition timing. The results show thatcertain ignition timing can be found where COVIMEPis minimal in given operationconditions. As fixed ignition timing pattern is used, different ignition timings lead todifferent results of cyclic combustion variations characteristics. However, the resultis unique when using MCV ignition timing pattern.As well as that, the combustion of methane and hydrogen mixture was simulatedby Chemkin. For studying the sensibility of critical ions and the concentrationdifferences of ingredient, mechanism for methane combustion was reduced and ionic reactions were partitioned by different pathways. The results show that the ions suchas H and OH are most impact on the reaction of methane and hydrogen mixture.Hydrogen blend could reduce the amount of CO2.At last, with OpenFOAM, the combustion mechanism of methane and hydrogenmixture was analyzed by modeling constant volume combustion bomb, simulatingthe burning of the mixture and proofreading the results. The research reveals thathydrogen blend could enhance the combustion performance of methane mixture butincrease the amount of NO. The raise of activation energy makes the reaction ratemore sensitive to the temperature changes.