This article is an overview of a φ (equivalence ratio) - T (temperature) map and its applications for studying engine combustion concepts. The φ-T map gives visual image of in-cylinder condition of engine combustion and is utilized to study various engine combustion concepts in the last ten years. In the first part, the background and calculation method of the map are described. In addition, 6 combustion regions, namely, CDC (Conventional Diesel Combustion), LTC (Low Temperature Combustion), HCCI (Homogeneous Charge Compression Ignition), SLRC (Smokeless Rich Combustion) , SI (Spark Ignition) and DP (Desirable Path) are defined on the map. In the second part, several combustion concepts and those combustion regions on the map are discussed to show the point of contact between the φ-T map and engine combustion concepts.
Analysis from both experimental and theoretical viewpoints of the formation of particulate matters (PM) in a gasoline engine is strongly required due to stringent regulations and improvement of atmospheric pollutions. As a gasoline engine usually takes premixed combustion, it was thought that PM would not be a problem. However, as a direct fuel injection system is getting popular, PM formation sometimes becomes a problem during cold start and taking stratified combustion like diesel combustion. In this article, research review in both experimental and theoretical analyses is made. At this moment, unfortunately, we found we do not have enough information on this issue. Further research on this issue is now strongly required to clarify the phenomenon.
It is well-known that the deposits accumulated excessively in automobile engine affect the exhaust emission and drivability. Accordingly, the accumulation of the deposit is one of the serious problems to be solved for developing high performance engines. We have been studying the analytical methods of the deposit formation in order to clarify the cause of the deposit accumulation. The methods introduced in this documentation are as follows. First, the deposits were classified into two types of seven components by the differences in their formation origins and environments; four components from fuel, three components from engine oil. Next, the characteristics of these components were determined by four kinds of analytical techniques, and the seven components could be distinguished from one another by four kinds of analytical indexes; chemical structure, elemental composition, thermal gravimetric property and solubility. Furthermore, by using these indexes, the deposit formation factors such as formation origins, formation environments and formation routes could be estimated. In addition to the above methods, the key points to keep in mind for the deposit countermeasure were also described.
This paper reviews a part of studies on flame spread over a combustible solid with a focus on modeling approaches to the phenomenon. By reviewing the de Ris theory and a simplified version of it, it is first discussed that the spread rate is an eigenvalue, and its determination requires an eigenvalue relationship. Smoldering propagation without flame is also discussed. When smoldering propagation occurs because of limited oxygen supply, fingering instability often appears. The mechanism of fingering instability is similar to that of diffusive-thermal instability of gaseous premixed combustion, and therefore the Lewis number is a key parameter. Considering smoldering propagation in a narrow space, the definition of an effective Lewis number of smoldering propagation is proposed, and the results of numerical simulations and experiments are compared at two different effective Lewis numbers.
An internal combustion engine with laser breakdown ignition was operated under inert gas and exhaust gas dilution, and the influence of increased dilution rate on engine performance and emissions was clarified. As a result of this experiment, operating range was expanded in proportion to specific heat ratio of inert gas and exhaust gas. And at high dilution rates, the gasoline engine operation was more stable with laser-induced breakdown ignition than with conventional spark ignition, since the IMEP was higher and the COVIMEP was lower with laser ignition.
For deflagration to detonation transition (DDT), several explanations on initiation have been given. Nevertheless, the knowledge on DDT is still insufficient for predicting where and when detonation occurs. In order to improve the reproducibility, an ethylene oxygen mixture was ignited forcibly by spark discharge behind an incident shock wave near the wall. The process of flame development was visualized by Schlieren imaging and analyzed by drawing several wave element trajectories on the shock waves ahead of the flame. As a result of varying the timing of spark discharge, detonation initiation was promoted as the boundary layer Reynolds number Reign increases. For Reign of more than 5.0 × 106, DDT was caused at 45 ± 10 μs. The processes of flame development were classified as Mode 1 and 2, which denote Reign of less than transition Reynolds number and more than it, respectively. Although the times for detonation initiation were markedly different in Mode 1 and 2, it was found that the both flame developments were similar. The accelerated flame near the wall propagates in upstream direction along the wall, resulting in approaching the shock wave front. This makes the shock stronger by coalescing of numerous compression waves. As the strengthened shock compresses the unburned gas, the flame was more accelerated, so that at the position where the flame front reached the shock front detonation initiation occurred. The difference of flame development between Mode 1 and 2 was observed in the initial stage in particular in the early 20 μs. Detonation initiation was caused at the position where following three conditions were satisfied: (1) A local Mach number reaches 2.4. (2) The flame front approaches and reaches the shock front ahead of it. (3) A concavity is generated on the flame/shock front, compressing the unburned gas coming into the point.
In case of diffusion combustion, a well-known “lifted flame” is formed. So far, we have focused on a combustion field in a triple-port burner. In the triple-port burner, since there are two boundaries of fuel and air, two flames are formed. Dependent on the flow condition, four flame configurations are observed, which are, (i) attached flames, (ii) inner lifted/outer attached flames, (iii) inner attached/outer lifted flames, (iv) twin lifted flames. Then, it is possible to study the interaction between two flames, which could give us useful information on turbulent flames. By changing flow conditions, we have investigated the transition between the attached flame and the lifted flame both by experimentally and numerically. In this study, by PIV/OH-PLIF simultaneous measurements, we examined the flow field and liftoff height of stationary and nonstationary flames. Results show that, as the liftoff height is larger, the minimum axial velocity around a base of the lifted flame increases. Also, the hysteresis characteristics of the inner and outer lifted flames are confirmed.
First-principle computations were performed to investigate the methanol surface reactions on various metal surfaces. The adsorption energy of methoxy intermediate was shown to be dependent on the electronegativity of surface atoms. This was found to affect the reaction pathway and the reactivity of surface methanol reactions. It was confirmed that surfaces composed of high electronegativity atoms, such as Pt, destabilize the methoxy intermediate and increase the total methanol decomposition rate. The effect of surface oxygen atom on the methanol decomposition was also investigated. It was found that the surface oxygen atoms promote O-H bond scission and hinder C-H bond scission. Based on the first-principle computational results, methanol/Pt surface reaction model was constructed and used to investigate the mechanism behind the hot-surface ignition of methanol/oxygen mixture. Numerical simulation using combined gas-phase and gas-surface reaction model showed that hot Pt surface highly promotes the ignition of the methanol/oxygen mixture, but only slight promotion was observed in the case of methane/oxygen mixture. The cause of the difference was found to be the rate of heat production due to fuel oxidation reaction at Pt surface.