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Numerical and Experimental Analysis of Homogeneous Charge Compression Ignition with Normal Paraffins, Branched-chain Paraffins and Aromatics Combined Fuels

Reyhanian, Masoud | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54939 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Hosseini, Vahid; Mozafari, Ali Asghar
  7. Abstract:
  8. The purpose of this dissertation is to experimentally and numerically investigate the effect of molecular structure, composition, and physical and chemical properties of fuel on HCCI combustion. A well-equipped laboratory was set up to perform the required tests, capable of performing HCCI tests with different fuels. All tests used a single-cylinder diesel engine modified to operate in HCCI mode. Also, for numerical simulation, a chemical kinetic multi-zone model was developed to predict HCCI combustion behavior with appropriate accuracy. To investigate the effect of fuel chemical structure on HCCI combustion, three fuels, toluene, iso-octane and normal heptane, with entirely different chemical structures, were used. Three different combinations of these fuels, namely TRF0, TRF30, TRF54 (containing 0%, 30% and 54% toluene, respectively) were selected so that the research octane number for all three of these combinations was 70. The results showed that TRF0 fuel has the lowest start of combustion at higher intake pressures, but by reducing the intake pressure, the combustion time of TRF54 fuel becomes earlier than TRF0. At lower temperatures, by decreasing the toluene content of the fuel, the start of combustion is advanced. But with increasing temperature, this trend is reversed. Sensitivity analysis for the normal heptane and toluene fuel blends showed that the chemical kinetic mechanism of toluene becomes more important at high temperatures, and decomposition of benzyl peroxide is the most important reaction at high temperatures; Therefore, toluene at higher temperatures helps to advance the start of combustion.A new numerical method was developed called the artificial species method to separate the chemical, thermodynamic and dilution effects of adding additive fuels to the base fuel. Iso-octane, normal heptane and methane fuels were used as base fuel and RG fuel containing 75% H2 and 25% CO was used as additive fuel. It was observed that the chemical effects of CO and H2 in each fuel are very different. In normal heptane, hydrogen is responsible for almost all of the chemical effects of RG, and CO has no role. In iso-octane combustion, the chemical effect of RG is negligible, while both CO and H2 slightly advance the combustion. The interaction of CO and H2 in methane combustion is significant. At RG = 30%, their interaction causes the combustion to advance by 1.8 degrees crank. This means that if CO is added to methane alone, it delays combustion, but combustion advances in the vicinity of H2 due to the activation of new reaction pathways
  9. Keywords:
  10. Homogeneous Charge Compression Ignition (HCCI) ; Low Temperature Combustion ; Chemical Kinetic ; Reactivity Controlled Combustion Ignition Engines (RCCI) ; Toluene Reference Fuel

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