Hiroshi Kawanabe

An Optimal Usage of Recent Combustion Control Technologies for DI Diesel Engine Operating on Ethanol Blended Fuels

The aim of this study is to find strategies for fully utilizing the advantage of diesel-ethanol blend fuel in recent diesel engines. For this purpose, experiments were performed using a single-cylinder direct injection diesel engine equipped with a high-pressure common rail injection and a cold EGR system. The results indicate that significant PM reduction at high engine loads can be achieved using 15% ethanol-diesel blend fuel. Increasing injection pressure promotes PM reduction. However, poor ignitability of ethanol blended fuel results in higher rate of pressure rise at high engine loads and unstable and incomplete combustion at lower engine loads. Using pilot injection with proper amount and timing solves above problems. NOx increase due to the high injection pressure can be controlled employing cold EGR. Weak sooting tendency of ethanol-blend fuel enables to use high EGR rates for significant NOx reduction. Above finding indicates that low level of PM and NOx emission with no fuel consumption penalty is achievable when diesel-ethanol blend is used with combination of modern combustion control methods.

Gas-flow measurements in a jet flame using cross-correlation of high-speed-particle images

Temporal variations of a two-dimensional distribution of velocities in a nitrogen jet and a methane-jet flame are measured by cross-correlation particle-image velocimetry (PIV). Two different approaches to investigating the turbulence characteristics are demonstrated. One gives the distribution of ensemble-averaged velocities and turbulence intensities by means of repetitive PIV measurements using a double-pulse laser for a longer period. The other provides the detailed motion of velocity profiles for a shorter duration, allowing one to analyse the characteristic scale of turbulence using a high-power continuous laser. The accuracy of measurements of the time-averaged velocity and turbulence intensity is quantitatively assessed on the basis of the agreement with the results from hot-wire-anemometry (HWA) measurement. This indicates the feasibility of the PIV measurement, which may supply information about turbulence characteristics. From the measured results for a jet and a jetting flame, it is shown that the velocity gradient in the shear layer in the reacting zone is increased due to the local acceleration caused by buoyancy, resulting in higher turbulence intensities than those in a non-reacting jet. Also, from the change in the distribution of velocity vectors with time, it is clear that the turbulence eddies are carried downstream along the gas motion with little transformation. The time scale of turbulence at each location in the flow is obtained from the autocorrelation function of the velocity fluctuations. Furthermore, this can afford an estimate of the turbulence length scale if one assumes that the Taylor hypothesis is valid and multiplies the time scale and the time-average velocity. It is shown that the characteristic length scales of a flaming jet are about 1.5 times greater than those of a non-flaming jet. The effects of combustion on the turbulence in a flaming jet are discussed in detail on the basis of these experimental results.

Computational fluid dynamics analysis of the combustion process and emission characteristics for a direct-injection-premixed charge compression ignition engine

The direct-injection-premixed charge compression ignition–based combustion process with a high exhaust gas recirculation ratio and early injection timing is simulated using a Reynolds-averaged Navier–Stokes–based commercial computational fluid dynamics code with a nonhomogeneous mixture auto-ignition combustion model. In addition, the formation processes of nitrogen oxide (NO), carbon monoxide (CO), and unburnt hydrocarbon are calculated. The calculation results are compared with the experimental data. According to the calculation results, the formation processes of NO, CO, and hydrocarbon are discussed in relation to the spray development and ignition point. Furthermore, the combustion process of two-stage injection is also calculated. The result shows that the combustion process is described well by this model except in the case where auto-ignition occurs in the squish area. Additionally, the relationship between the combustion process and the mixture distribution is clarified. The main origins of the unburnt hydrocarbon and CO emissions are located in the center region of the combustion chamber, where the mixture becomes excessively lean and low in temperature.

A study on premixed charge compression ignition combustion of natural gas with direct injection

Abstract In order to extend the available load range and obtain higher thermal efficiency in natural gas premixed charge compression ignition (PCCI) engines, a strategy for controlling direct injection combustion is discussed. Experimental results from single-cylinder engine tests demonstrate the possibility to extend load range by direct fuel injection. Reduced nozzle orifice size and reduced injection angle provide higher combustion efficiency; however, this promotes the tendency to knock because of the formation of a locally rich mixture. Arising from discussions based on prediction by computational fluid dynamics (CFD) code, considering mixture heterogeneity, it is suggested that controlling probability density functions (PDFs) of fuel concentration could be a means to control the rate of pressure rise. Restricted air utilization is useful to activate combustion at low overall equivalence ratios; on the other hand, full utilization of in-cylinder air and formation of a quantity of lean mixture can provide mild combustion.

Numerical Analysis of Auto-ignition Process in a Non-homogeneous Mixture

An auto-ignition process of non-homogeneous mixture was fundamentally investigated using a numerical calculation based on the chemical kinetics and stochastic approach. In the present study, the auto-ignition process of n-heptane is calculated using a reduced mechanism developed by Seiser et al. The non-uniform states of turbulent mixing are statistically described using probability density functions and the stochastic method, which was originally developed based on Curls model. The results show that the starting points of the low temperature oxidation and ignition delay period are hardly affected by the equivalence-ratio variation, however, the combustion duration increases with increasing variance of equivalence ratio. Furthermore, the combustion duration is mainly affected by the non-homogeneity at the ignition and not very much affected by the mixing rate.

Improvement of Thermal Efficiency in a Diesel Engine with High-Pressure Split Main Injection

This study aims to utilize high-pressure split-main injection for improving the thermal efficiency of diesel engines. A series of experiments was conducted using a single-cylinder diesel engine under conditions of an engine speed of 2,250 rpm and a gross indicated mean effective pressure of 1.43 MPa. The injection pressure was varied in the range of 160–270 MPa. Split-main injection was applied to reduce cooling loss under the condition of high injection pressure, and the split ratio and the number of injection stages were varied. The dwell of the split main injection was set to near-zero in order to minimize the elongation of the total injection duration. As a result, thermal efficiency was improved owing to the combined increase in injection pressure, advanced injection timing, and split-main injection. According to the analysis of heat balance, a larger amount of the second part of the main injection decreased the cooling loss and increased the exhaust loss. Computational fluid dynamics calculations were performed to reveal the causes of the lower cooling loss; however, the results could not capture the experimental trend when using an ordinary spray cone angle. While using a wider spray angle for the second part of main injection, the calculated trend improved. The total cooling loss depends on the balance between the cooling losses by the first and second main sprays.

Analysis of flow and heat transfer during the impingement of a diesel spray on a wall using large eddy simulation

Numerical calculations were carried out to investigate the formation of a fuel–air mixture as well as ignition and combustion processes associated with a diesel spray impinging on a wall. This was performed by modeling the spray formed by injecting n-heptane into a constant-volume vessel under high temperature and pressure, with the fuel droplets described by a discrete droplet model. The flow and turbulent diffusion processes were calculated based on the large eddy simulation method to simulate the formation of a local non-homogeneous mixture and the accompanying heat release. The flame structure and heat transfer to the wall during impingement were also assessed. The results show that heat transfer to the wall is increased in the peripheral region around the stagnation point, as a result of the high temperature and thin boundary layer. Conversely, in the outer region, the heat transfer decreases as the boundary layer becomes more developed.

Automotive Internal Combustion Engines

To achieve further reductions in fossil fuel consumption and carbon dioxide (CO2) emissions, the transportation sector will need to assume a key role. Based on the BLUE Map scenarios for 50 % reduction in CO2 emissions by 2050 in the Energy Technology Protocol 2010 of the International Energy Agency, conventional engine vehicles and hybrid electric vehicles (HEVs)—including plug-in hybrid electric vehicles (PHEVs)—are expected to account for 90 % of the market and will still account for 50 % of the market by 2050. This means that it is important that thermal efficiency of the internal combustion engine (ICE) be increased. Research and development into high-efficiency ICEs has been progressing in Japan, Europe, and the United States. In this paper, current research status and future prospects of ICEs and HEVs (PHEVs) are described.

Factors Determining Antiknocking Properties of Gaseous Fuels in Spark-Ignition Gas Engines

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.Copyright

Factors Determining Anti-Knocking Properties of Gaseous Fuels in Spark Ignition Gas Engines

The factors affecting knock resistance of fuels, including hydrogen (H2), ethane (C2H6), propane (C3H8), normal butane (n-C4H10), and iso-butane (i-C4H10), were determined using modeling and engine operation tests with spark-ignition gas engines. The results of zero-dimensional detailed chemical kinetic computations indicated that H2 had the longest ignition delay time of these gaseous fuels. Thus, H2 possessed the lowest ignitability. Results of engine operation tests indicated that H2 was the fuel most likely to result in knocking. The use of H2 as the fuel produced a temperature profile of the unburned gas compressed by the piston and flame front that was higher than that of the other fuels due to the high specific heat ratio and burning velocity of H2.The relation between knock resistance and secondary fuel ratio in methane-based fuel blends also was investigated using methane (CH4) as the primary component, and H2, C2H6, C3H8, n-C4H10, or i-C4H10 as the secondary components. When the secondary fuel ratio was small, the CH4/H2 blend possessed the lowest knocking tendency. But as the secondary fuel ratio increased, the CH4/H2 mixture possessed a greater tendency to knock than did CH4/C2H6 due to the high specific heat ratio and burning velocity of H2. These results indicate that the knocking that can occur with gaseous fuels is not only dependent on the ignitability of the fuel, but it also the specific heat ratio and burning velocity.Copyright