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Numerical Simulation of Spray and Combustion in a Gasoline Direct Injection (GDI) Engine

Zamani Haghighi, Hamed | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45447 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Hosseini, Vahid; Afshin, Hossein
  7. Abstract:
  8. Energy crisis is one of the crises which human beings face these days. Optimizing the operation of energy consuming machines is one of the most effective methods in decreasing energy consumption. Gasoline direct injection engines as new achievements in automobile and propulsion industry, reduce fuel consumption by increasing the engine efficiency. In these types of engines, a high pressure injector injects fuel directly into the combustion chamber instead of injecting fuel in intake ports. Thus, because of evaporation cooling, the mixture cools down, so the possibility of achieving higher compression ratios in higher engine speeds and loads, without occurrence of knock is provided. Increase of compression ratio increases the engine thermal efficiency. In low speeds and loads, by removing throttling valve and creating stratified mixture fuel consumption is reduced.
    In this research, primary and secondary breakup sub models for simulating fuel spray were firstly developed. Using these sub models, the injected fuel spray from a 6-hole direct injection injector into a constant volume vessel was simulated and then by comparing the results with experimental data, spray sub models were calibrated. Then, using AVL Fire code dynamic mesh of National engine chamber was generated and mixture entering the chamber and combustion was simulated. In this case, combustion model coefficients were calibrated by comparing numerical results with experimental data. In the next step, the simulated spray was placed in the chamber in order to inject fuel directly using spray-guided strategy. Finally, the effect of delay in start of injection time and reduction of equivalence ratio on the combustion was investigated.
    Spray simulation results show that primary and secondary breakup sub models should be calibrated for each injector separately. In case of multi-hole injectors, all jets emerging from all nozzles should be simulated simultaneously so as to have authentic results. Combustion simulation results show that in case of forming stoichiometric mixture, fuel should be injected early to create homogenous mixture and mixture combustion becomes complete. Late injection of fuel causes inappropriate mixing of fuel and air, spray-wall impingement, fuel wall-film and so incomplete mixture combustion. As a result, power production is reduced and emission formation increases. In addition, for using advantages of lean combustion, effective parameters on mixture formation and combustion such as injector location in chamber, direction of fuel injection, start of injection, ignition timing and … should be properly modified
  9. Keywords:
  10. Fuel Spray ; Gasoline Direct Injection Engine ; Multihole Injector ; Homogeneous Mixture Combustion ; Stratified Mixture Combustion

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