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

Abstract

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 autoignition 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.

A new concept for high efficiency and clean diesel combustion by controlling mixture distribution with dual zone combustion chamber

“…We named this new combustion concept ''Distribution Controlled partially Premixed Compression Ignition (DCPCI).'' Regarding the bowl shape, the lower zone carried over our previous egg-shaped bowl concept to maintain the mixing enhanced by strong vertical vortex along the cavity wall, 20 whereas the upper zone adopted a smoothly curved shape to allow smooth mixture flow in the squish area. Enhancing mixing with strong vertical vortex is important for conventional diffusive combustion under higher load conditions.…”

“…In the shape, each spray that is injected relatively near TDC impinges on the piston lip area and is separated to the upper and lower zones so that interference between early stage sprays and subsequent spray and that between the burned gas formed by the early stage injections and the subsequent spray can be suppressed. We named this new combustion concept “Distribution Controlled partially Premixed Compression Ignition (DCPCI).” Regarding the bowl shape, the lower zone carried over our previous egg-shaped bowl concept to maintain the mixing enhanced by strong vertical vortex along the cavity wall, 20 whereas the upper zone adopted a smoothly curved shape to allow smooth mixture flow in the squish area. Enhancing mixing with strong vertical vortex is important for conventional diffusive combustion under higher load conditions.…”

Study of a hybrid pneumatic-combustion engine under steady-state and transient conditions for transport application

“…In order to potentially solve the problems including environmental pollution and the shortage of fossil fuels, various environmental-friendly automobile technologies have been proposed in the past few decades. In addition to the efforts on the design of combustion chamber, 1 fuel or water injection strategy 2–4 and alternative fuel, 5,6 the application of hybrid propulsion system is also one of the potential solutions to improve the overall energy fuel saving and reduce the emissions.…”