The "Innovative Combustion Technology" program, a national project is established under the Cabinet Office, Government of Japan as a part of the" Cross-ministerial Strategic Innovation Promotion Program (SIP)". The "Gasoline Combustion Team" is one of teams of the "Innovative Combustion Technology" program.
The "Gasoline Combustion Team" is comprised of Keio University as a Leader university and 29 universities as a Cluster university. Upon agreement with the Japan Science and Technology Agency (JST), we have been conducting the research on the "Super-Lean Burn for Gasoline Engines" with a support of the Research Association of Automotive Internal Combustion Engines (AICE) under the strong industry, academia and government collaboration.
This paper introduces both scientific and technological approaches to innovative combustion technologies to realize the "Super- Lean Low Temperature Combustion", targeting a thermal efficiency of 50%.
Research activities on advanced combustion control for diesel passenger car engines are presented, which are part of SIP"innovative combustion technologies" supported by Council for Science, Technology and Innovation. The research aims at developing combustion technologies which enable 50% maximum thermal efficiency at high loads and CO2 reduction at part loads. The major concept for higher thermal efficiency is simultaneous realization of higher degree of constant volume and lower cooling loss. For the middle- and low-load CO2 reduction, wide-range PCCI combustion is pursued. Technologies are also investigated to mitigate the increase in combustion noise brought by the above-mentioned combustion concepts. As a result, the basic ideas and technologies were proposed for advanced combustion control, and the knowledges were accumulated for related phenomena; inverse-delta injection rate for eliminating rich mixtures in a spray flame, penetration and dispersion control of spray flame for reduced cooling loss, lean combustion for controling PCCI using ultrahigh injection pressure, and combustion noise reduction by combination of heat release rate control and shift of vibration frequency of engine parts. In addition, several numerical models have been developed for spray formation, oxidation of larger hydrocarbons, combustion noise and so on.
The control team was divided into three groups: control group, CAE group, and PM group. The goal addressed by this team is the development of modeling and control techniques that contribute to 50% thermal efficiency. When implementing the new combustion method, there is a possibility that the performance can’t be achieved due to the influence of the disturbance, etc., and an intelligent control system that can be controlled in real time is needed. The control group developed "Model Based Control" based on a mathematical model that represents the underlying physical and chemical phenomena as closely as possible for diesel engines with advanced combustion technology. On the other hand, the CAE group developed a next-generation 3D engine combustion software "HINOCA" capable of high-speed calculation by integrating various sub-models and platforms for gasoline engines. Furthermore, the PM group developed a technology that can predict the amount of PM generation in exhaust gas generated from a gasoline engine at cold start, and developed the state-of-the-art measurement technology and proposed PM generation mechanism. Based on these fundamental studies, PM model was completed.
Loss Reduction Team in the SIP’s “Innovative Combustion Technologies” has been focusing on utilizing the exhaust gas energy and reducing mechanical losses in theory and practice in order to contribute to achieving a 50% brake thermal efficiency targeted in both 2.0 L automotive gasoline and diesel engines. Major components of the turbocharging system were optimally redesigned based on 3D CFD modeling validated by measurements. A thermoelectric system was developed to utilize the energy of the exhaust gas downstream of the turbocharger outlet. A device BiTe was chosen for an exhaust gas temperature range of 200℃ to 300℃. The number and layout of the modules were optimized by using a heat transfer model taking into account the entire engine cycle thermal efficiency. Major moving components were also improved to simultaneously lower their friction forces and avoid wear and seizure using special surface treatments and low viscosity oils with additives, resulting in achieving up to a 55% friction reduction compared with the baseline. Detailed numerical models and measurement methods have been developed to explain and predict these improvements. Eventually, the team could increase the bake thermal efficiency by 3.5%pt and 3.0%pt in the gasoline and diesel engines, respectively.
Fundamentals of Particle Image Velocimetry (PIV) are introduced. The paper describes short historical story of the PIV. The origin of the word of the “PIV” is seen in the paper described by Adrian (1984). The PIV techniques are based on the flow visualization. The velocity measurement methods based on the flow visualization are also introduced. Particle Streak Velocimetry (PSV), Laser Speckle Velocimetry (LSV), Particle Tracking Velocimetry (PTV), and PIV have been used for flow velocity measurements. Differences among these methods are explained. Basic construction of PIV and timing chart of image acquisition are shown. While normal PIV used only one camera for measuring two-dimensional velocity components in a measurement plane, multiple cameras are used for extended measurements of three-dimensional velocity components. The concepts of the extended PIV is also explained. Several measurement results are introduced. Flow around a cylinder, flow around a car model, and in-cylinder flow are shown as basic results by PIV. Spray flow is shown as an example of a combination measurement of PIV and Laser Doppler Anemometry (LDA). Laser Induced Fluorescence (LIF) method presents a brightness distribution in the thin fluid film. The combination of LIF and PIV is applied to measure oil film behavior on the piston skirt in the model engine. These results by simple and complex measurement techniques are shown in last parts.
In order to clarify the relationship between flame and turbulent flows in various combustion devices, it is one of the important factors to consider from the viewpoint of the fine scale structures of turbulent flow. In this article, direct measurement of turbulent fine structure by multi-plane stereoscopic particle image velocimetry (PIV) is introduced, and the measurement techniques, such as Stokes number of seeding particles, spatial resolution of PIV, calculation method of velocity gradients, are discussed from the fine scale structure of turbulent flow. Furthermore, the estimation method of turbulence characteristics by using single plane PIV is explained using the case of micro PIV for an optical gasoline engine in recent years.
This study investigated the characteristics of the response of a lean methane-air premixed flame to sinusoidal oscillation of the equivalence ratio. The oscillation frequency was varied from 5 to 50 Hz. The mean equivalence ratio and fluctuation amplitude were 0.85 and 0.05, respectively. In the low frequency range, the oscillation amplitudes of the flame position xf, burning velocity Su, velocity gradient g, and preheat zone thickness δp responded quasi-steadily to the equivalence ratio oscillation. However, in the high frequency range they responded unsteadily: that is, the fluctuation amplitude of xf became less than that of the static flame, but the oscillation amplitudes of Su, g, and δp exceeded those of the static flame with respect to frequency over the same equivalence ratio fluctuation range, and these values peaked at 40 Hz. The increase in oscillation amplitude of Su with respect to frequency was likely a result of the dynamic characteristics of the flame movement, mass transfer from unburned gas to the side of the flame, and the preheat time of the mixture.
Near-limit flame spread is a topic of extensive fire research, and recent studies pointed out that near-limit flame spread characteristics were significantly affected by flame instability. This study considers opposed-flow flame spread in a narrow channel, in which oxygen supply by natural convection is suppressed, leading to near-limit conditions. Fingering instability appears when the oxidizer flow velocity or the channel height is small. A major objective of this study is to numerically examine the influence of fingering instability on the flame spread velocity and the extinction limit. Three-dimensional basic equations are first developed and then reduced to two-dimensional ones considering the narrowness of the domain. Numerical solutions of the two-dimensional model, in particular, fingering patterns and flame spread velocities are compared with previous experimental data, and reasonable agreement between them is confirmed. Traveling wave solutions for one-dimensional basic equations are then obtained and compared with the corresponding two-dimensional solutions. It is found that the two-dimensional flame spread velocity is faster than the one-dimensional value because the reaction is enhanced by instability. It is also found that two-dimensional flame spread is possible under certain conditions for which extinction occurs in one-dimensional flame spread. Dependence of flame spread velocity and extinction limit on model parameters is finally discussed based on predictions of the one-dimensional model.