Two-dimensional direct numerical simulations (2D DNS) are used to study auto-ignition of nheptane/air mixture with charge and temperature stratifications under elevated pressure and temperature conditions relevant to PCCI (Partially-premixed Charge Compression Ignition) engines. Detailed species transport and a skeletal n-heptane chemical kinetics mechanism are employed; the effect of compression/expansion due to piston motion is also taking into account. The result shows that charge and temperature stratifications have an important impact on the ignition delay and the spatial structure of the reaction zones regardless the initial mean temperature (T 0) is within or outside the negative temperature coefficient (NTC) regime. The second-stage ignition delay time decreases as charge stratification increases but it increases with increasing temperature stratification. Larger charge stratification can spread out heat release due to the high sensitivity of ignition delay time to the equivalence ratio (φ) and the temperature gradient. Furthermore, stronger turbulence can homogenize mixture fluctuations, but the ignition delay time is similar as that in weak turbulence case because the species diffusion rate is rather weak compared with chemical reaction rate. A series of 1-D simulations are carried out under different T 0 and T-φ correlations to investigate their effect on the combustion process.

Two-dimensional direct numerical simulation (2-D DNS) is used to investigate the effect of turbulence intensity and composition stratification on H2/air mixture auto-ignition in a constant volume enclosure relevant to homogeneous charge compression ignition (HCCI) engines. Different turbulence levels, composition fluctuations, EGR (Exhaust Gas Recirculation) ratios, initial pressure, domain lengths and energy spectra are simulated with detailed analysis in ten 2-D DNS cases. The results show that the ignition delay time tends to be prolonged and the heat release rate increased under higher turbulence intensity. Turbulence can affect the reaction zone, e.g., through wrinkling of reaction front and enhancement of mixing and heat transfer. Higher composition stratification can smoothen the overall heat release rate and shorten the ignition delay time. Budgets terms and Probability Density Function (PDF) of density weighted displacement speed show that in HCCI engines flame propagation can co-exist with volumetric auto-ignition. As expected, lower pressure leads to thicker flame thickness and longer ignition delay time. Increasing EGR ratio has a negative influence on the formation of OH reaction, resulting in a longer ignition delay time. Two energy spectra with respect to low and high Reynolds number are compared to show a discrepancy on ignition delay time due to different kinetic energy dissipation rates.

In spark assisted homogeneous charge compression ignition (SACI) engines a premixed flame is first established; the propagating flame results in compression heating of the end gas and finally autoignition of the gas. Two dimensional direct numerical simulation (2D DNS) and one dimensional (1D) detailed simulations of flame/spontaneous ignition interaction in a lean hydrogen/air mixture under a constant volume enclosure relevant to SACI engine conditions are performed using detailed chemistry and detailed transport properties. In a 2D outward propagating spherical flame, thermaldiffusive instability is observed and once auto-ignition starts a low temperature region in the preheat zone of the flame is formed. Subsequently, the ignition in the preheat zone is suppressed. Then 1D flame/ignition interactions in H2/air, syngas/air and methane/air mixtures are studied using detailed numerical simulations. The results reveal that due to preferential diffusion of hydrogen, heat and mass transfer in the preheat zone inhibits the ignition process, yielding a slower reaction rate hence an even lower temperature in the region. It is shown further that the low temperature region is not affected by the domain size and one step chemistry but it will disappear at very low initial temperature conditions. This is due to the absence of auto-ignition under low temperature conditions.

The computer aided measuring system is established to evaluate geometrical information of the structure in subsection manufacture. The cloud points data of surface are collected by laser tracker so as to explore continuing data processing software and evaluate the error of dimension and shape, and then the real measuring model, matched by the corner information, is compared with CAD through the best-fit algorithm. The lack of fitting information which will cause the low measuring precision is solved by the least square method constrained by radius in structure with large radius and small central angle. As the research object, the tunnel structure is used in the quality control of manufacturers.