Minoru Iida

Expanding the HCCI Operation With the Charge Stratification

A single cylinder CFR research engine has been run in HCCI combustion mode at the rich and the lean limits of the homogeneous charge operating range. To achieve a variation of the degree of charge stratification, two GDI injectors were installed: one was used for generating a homogeneous mixture in the intake system, and the other was mounted directly into the side of the combustion chamber. At the lean limit of the operating range, stratification showed a tremendous improvement in IMEP and emissions. At the rich limit, however, the stratification was limited by the high-pressure rise rate and high CO and NOx emissions. In this experiment the location of the Dl injector was in such a position that the operating range that could be investigated was limited due to liquid fuel impingement onto the piston and liner.

A Computational Investigation into the Cool Flame Region in HCCI Combustion

Multi-dimensional computational efforts using comprehensive and skeletal kinetics have been made to investigate the cool flame region in HCCI combustion. The work was done in parallel to an experimental study that showed the impact of the negative temperature coefficient and the cool flame on the start of combustion using different fuels, which is now the focus of the simulation work. Experiments in a single cylinder CFR research engine with n-butane and a primary reference fuel with an octane number of 70 (PRF 70) were modeled. A comparison of the pressure and heat release traces of the experimental and computational results shows the difficulties in predicting the heat release in the cool flame region. The behavior of the driving radicals for two-stage ignition is studied and is compared to the behavior for a single-ignition from the literature. Model results show that PRF 70 exhibits more pronounced cool flame heat release than n-butane. Such a tendency agrees with experimental data.

Predictive Simulation of PFI Engine Combustion and Emission

This paper reports a methodology to estimate combustion pattern and emission by predictive simple simulation with good accuracy on various conditions of PFI engine. 3D-CFD cord VECTIS has been applied for this simulation, its settings and methods are as follows. RANS equation with liner k-epsilon model has been used as the turbulence model. Turbulent burning velocity equation contains not only turbulent velocity term but also laminar burning velocity term. For ignition model, we use a predictive model called DPIK. We iterate cycle calculation until wallfi lm behavior is stabilized to get the reasonable mixture formation. We have applied this methodology to 125cc engine of motorcycle. As a result, we have obtained heat release curve and pressure curve with good accuracy on various operating conditions such as engine speed, engine load, air fuel ratio, wall temperature, and spray direction. CO and NOx calculated simultaneously have also been acceptable. CO formation is based on chemical equilibrium, and NOx formation is based on the extended Zeldovich mechanism. Using these results obtained by this methodology, optimal air-fuel distribution that aff ects heat release pattern and emission formation is suggested.