Motoshi Kataoka

Effect of combustion chamber shape on tumble flow, squish-generated flow and burn rate

Abstract Effects of squish area location on tumble and squish flow were investigated to control the knock in an SI engine. For the exhaust squish piston, tumble flow is collapsed by the exhaust squish clearance during the compression stroke, so that the compression-squish flow is strong. For the intake squish piston, tumble flow impinges on the edge of squish area and the induction of it into the squish area is controlled. The compression-squish flow is weakened and reverse-squish flow grows strong. This led to realization of a high heat release at late stage combustion. Simultaneously, the decrease of cycle-by-cycle variation of initial burn is realized. Consequently, knocking is controlled compared with a flat piston.

Simultaneous improvement of exhaust emissions and fuel consumption by optimization of combustion chamber shape of a diesel engine

In order to achieve clean exhaust gas emissions and high fuel efficiency in diesel engines, a new combustion chamber concept called “egg-shaped piston bowl” was proposed and its effectiveness was validated by engine experiments using a single-cylinder research engine. Numerical simulations of combustion processes and exhaust gas emissions were carried out on different piston bowl geometries using GTT-CHEM code, which is a three-dimensional computational fluid dynamics code coupled with detailed chemical kinetics. In this code, a combustion model taking account of the auto-ignition process of a non-homogeneous mixture and a detailed phenomenological soot model was incorporated. In the detailed phenomenological soot model, particle inception from polycyclic aromatic hydrocarbons, surface growth/oxidation and particle coagulation processes were considered. In addition, to investigate the soot formation characteristics with different piston bowl geometries, experimental measurements by the two-color method were conducted with a constant-volume vessel under high-temperature and high-pressure conditions. As a result of the engine experiments and the numerical simulations, it was confirmed that simultaneous reduction in exhaust gas emissions and fuel consumption was able to be achieved by the egg-shaped piston bowl concept.

Mazda’s New Common Rail DI Diesel Engine

The 2-litre 4-cylinder diesel engine develops 100 kW of power and 310 Nm of torque thanks to its high-pressure common rail system. The mid-sized passenger car equipped with this engine meets the Euro 4 exhaust standards and provides excellent NVH performance with multiple injection technology.