A multi dimensional model for the simulation of flow and combustion in combustion chamber was extended to knock calculation by coupling turbulence combustion model with simple chemical kinetics model. A Flamelet model proposed by Tahry that based on the probability of finding the flame and take into account of the strain rate has been implemented for the accurate prediction of flame propagation in homogeneous-charge turbulent pre-mixed combustion. A Shell model proposed by Halstead, modified to satisfy the principle of mass conservation and conservation of oxygen atom was used for knock calculation and combined with the Flamelet model to estimate the knock onset location and the timing. Visualizations were performed in order to verify the calculation accuracy for flame propagation and knock onset location. Flame propagation was visualized in an optical access engine, while knock detection was visualized in an actual engine. Moreover, the Effects of in cylinder flow on knock onset location were examined at different conditions such as tumble, reverse tumble and swirl flow field. The results confirmed that the calculations predicted flame propagation well. Simulation of the knock onset location was also shown to be possible. Applying this calculation to different in cylinder flow conditions, these were show that in cylinder flow affects knock onset location greatly. Furthermore, these calculations well agreed with experimental results.
Lean premixed combustion is one of the attractive ways to reduce nitric oxide emission as well as greenhouse gases from combustion devices, and the industrial demand on lean premixed combustion seems expanding to the field of regenerative combustion or heat recovery combustion where premixed combustion has not been attempted due to the fear of auto-ignition or flash-back. For the purpose, we have developed a unique mixing nozzle to create a quasi-premixture of fuel and air by rapid mixing, and applied this rapid mixing nozzle to an opposed jet type and a Bunsen type burners to observe combustion characteristics of the quasi-premixture. As a result, the quasi-premixed flame showed the same flame structure and combustion characteristics as the perfectly premixed flame even though the mixing time was extremely short as a few milliseconds. Therefore, the rapid mixing nozzle in this paper can be used to imitate highly preheated premixed flames, which may be impossible in a usual way, that is, the quasi-premixture of fuel and highly preheated air can be a substitution for highly preheated premixed combustion as far as the mixing time is shorter than the ignition delay of the fuel.
The coflow diffusion flame of the fuel mixture of carbon monoxide, hydrogen and nitrogen (CO-H2-N2) vs. air was simulated numerically with detailed chemistry, and its structure and NOx formation mechanism were investigated. They were compared with the flame of the mixture of hydrogen and nitrogen (H2-N2) vs. air, and the flame of the mixture of methane and nitrogen (CH4-N2) vs. air whose adiabatic flame temperatures for stoichiometric mixtures are identical with that of the CO-H2-N2 flame. Their flame structures including NOx distribution were measured experimentally and were compared with the numerical results for checking the validity of the adopted kinetic models. As a result, it was found that the temperature distribution and the length of the CO-H2-N2 flame are similar to those of the H2-N2 flame, but much different from those of the CH4-N2 flame. The NOx emission of CO-H2-N2 flame is the lowest among the three since the prompt NO is absent and the maximum temperature is considerably lower than H2-N2 flame due to the lower concentration of H2 that causes the preferential diffusion effect near the base of the flame. It was also found that the CO-H2-N2 flame has double consumption zones of CO along the flame surface, and the inner zone is due to the conversion from CO to H2.