Kazunari Kuwahara

Diagnostics of in-cylinder flow, mixing and combustion in gasoline engines

In a premixed leanburn engine employing an in-cylinder rotating flow, tumble, the influence of the in-cylinder flow field structure on combustion was investigated with a two-dimensional PTV, a three-dimensional PTV and the analysis of continuous and cycle-to-cycle UV flame images. As a result, optimum combustion control was achieved by controlling the generation of turbulence. In a gasoline direct injection engine adopting a wide spacing layout, the characteristics of mixture preparation were investigated by visualizing a fuel spray with laser shadowgraphy and LIF, and deriving the mixture strength at the spark plug from spectrum analysis of spark discharge emission. Also, the combustion characteristics were investigated by analysing flame emission spectra continuously, and imaging UV luminescence and thermal radiation of flame emission simultaneously. Consequently, it was clarified that combustion control is achieved by controlling air-fuel mixing.

Reduction of Reaction Mechanism for n -Tridecane Based on Knowledge of Detailed Reaction Paths

A detailed chemical kinetic mechanism for n-tridecane generated by KUCRS, contains 1493 chemical species and 3641 elementary reactions. Reaction paths during ignition process for n-tridecane in air computed using the detailed mechanism, were analyzed with the initial temperatures of 650 K, 850 K, and 1100 K in the τ1 dominant, negative temperature coefficient, and non-τ1 regions, respectively. Based on full knowledge derived from the reaction path analysis, a reduced mechanism containing 49 species and 85 reactions, was developed and validated. The reduced mechanism includes C3H7, C2H5, and CH3 as representative fragmental alkyl radicals, C7H14, C3H6, and C2H4 as representative alkenes, and C3H7CHO and CH2O as representative aldehydes. Ignition delay times with different initial temperatures between 600 K and 1200 K using the reduced mechanism, and their dependences on pressure and equivalence ratio agree well with those using the detailed mechanism. The profiles of fuel, CH2O, H2O2, and CO concentrations agree roughly with those using the detailed mechanism.

Factors Determining Antiknocking Properties of Gaseous Fuels in Spark-Ignition Gas Engines

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.Copyright

Factors Determining Anti-Knocking Properties of Gaseous Fuels in Spark Ignition Gas Engines

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.Copyright

Three-Dimensional In-Cylinder Flow-Field Structure before and after Distortion of Tumble.

The influence of tumble intensity on the three-dimensional flow-field structure was analyzed numerically using the STAR-CD code. It was found that when the tumble intensity is extremely high, because the velocity component in the direction of the axis of tumbling air motion is small, the flow-field structure can be treated as two-dimensional. When the tumble intensity is moderate or weak, however, various flows in the direction of the tumble axis can be observed. Therefore, such a flow-field structure should be treated as three-dimensional. A new method to measure the three instantaneous velocity components from a two-dimensional photograph was developed. By using three laser sheets composed of two continuous and one pulse laser light source with different colors radiated for preset durations and timings, velocity in the direction of the laser sheet depths can be derived. Employing this method, the flow-field structure at 15°BTDC was analyzed. It was confirmed that the distortion of tumble induces horizontal vortices in addition to the vertical vortex.