Unsteady Numerical Analysis on PCCI Combustion Affected by Intentional Initial Fuel Concentration Distribution

Unsteady numerical analyses were carried out for the PCCI combustion realization on the next generation diesel engine. The effects of intentional initial fuel concentration distribution on the ignition timing and the expansion of the operable range were focused. The numerical code was originally developed to analyze the unsteady combustion behavior of premixed gas with intentional initial fuel concentration distribution in the combustion chamber of PCCI engine. The fundamental equations for the numerical analysis are the Euler’s equations for compressible fluid, that consist of the conservation equation of mass, momentum, energy and chemical species. The equations are expressed in axisymmetric cylindrical (r-z) coordinate system. The time variation of the internal cylinder volume of the reciprocating crank-piston movement is expressed by the volume change rate, which is substituting the convection term in axial direction of the Euler’s equations. By using this technique, we can reduce the spatial dimension of the equations with keeping the consideration of volume change of the combustion chamber of reciprocating engine. The radial direction corresponds to the bore of the engine cylinder. By solving this equation system, we can consider the radial distribution in combustion chamber during the PCCI combustion such as temperature, mass fraction of chemical species, pressure, and so on. Detailed chemical kinetics with elementary reactions and multi-component diffusion for n-heptane system as fuel, ERC-mechanism, were considered. The NOx emission can be also considered by using the part of GRI-Mech3.0 for generation of thermal NOx. Totally, the 34 chemical species and 61 elementary reactions were considered. This code has a high resolution for time and space to capture the dynamic behavior in PCCI combustion such as a generation and propagation of shockwave causing detonation. A series of unsteady events on PCCI combustion can be simulated by considering the time variation of volume of combustion chamber varied with crank angle; such as the charged compression and auto-ignition of premixed gas, the flame propagation and the detonation with shockwave.