Daisuke Kawano

Improvement of combustion and emissions in diesel engines by means of enhanced mixture formation based on flash boiling of mixed fuel

Abstract A novel approach to reduce diesel engine emissions at relatively low injection pressures is proposed. This approach is based on the use of a mixed fuel where an additive or a low boiling point fuel such as CO2, gas fuel, or gasoline is mixed with a higher boiling point fuel such as diesel gas oil. When producing such a fuel, the vapour—liquid equilibrium in the two-phase region where the liquid and vapour phases of both components coexist is taken into account. In designing a mixed fuel, the authors intend to control both the physical process in the spray such as fuel evaporation and vapour air mixing and the chemical processes including spontaneous ignition and with reactions with regard to NO x , particulate matter (PM), and hydrocarbon (HC) formation. In this study flash boiling of mixed fuel is particularly focused on enhancing the mixing process in the spray because it has the potential to achieve fast evaporation and relatively lean and homogeneous mixtures. Experiments were carried out using two types of mixed fuel, both of which can generate flash boiling during injection events. In an experiment using a rapid compression machine (RCM) and an optical engine, mixed fuels consisting of liquefied CO2 as an additive and n-tridecane representing gas oil were employed with the aim of simultaneously reducting soot and NO x emissions. The high-speed images acquired for sprays reacting in the RCM and the engine clearly showed a significant reduction of soot formation in the spray. Reductions of soot and NO x emissions as well as the fuel consumption were also confirmed by emission measurements and a combustion analysis respectively. In other experiments, different types of mixed fuel consisting of gas or gasoline and gas oil were tested to see the effects on both the evaporation and ignition processes. The result of an engine experiment showed marked reductions of soot and HC emissions and fuel consumption.

Numerical analysis of Miller-premixed charge compression ignition combustion on a dynamic φ-T map

Abstract A variable valve timing mechanism has been applied in a high-speed direct injection diesel engine. The effective compression ratio (εeff) is lowered by means of late intake valve closing, while keeping the expansion ratio constant. Premixed charge compression ignition (PCCI) combustion, adopting the Miller cycle, was experimentally realized and numerically analysed. Significant improvements in NO x (nitrogen oxides) and soot emissions were achieved for a wide range of engine speeds and loads frequently used in a transient mode test. The operating range of the Miller-PCCI combustion has been expanded up to an indicated mean effective pressure of 1.3 MPa.

Emissions suppression mechanism of premixed diesel combustion with variable valve timing

Abstract A variable valve timing (VVT) mechanism is applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light-duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead centre are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of an effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, exhaust gas recirculation (EGR), supercharging systems, and high-pressure fuel injection equipment can simultaneously reduce NO x and smoke. The NO x and smoke suppression mechanism in the premixed diesel combustion is analysed using a three-dimensional computational fluid dynamics (3D-CFD) code combined with detailed chemistry. LIVC can achieve a significant NO x and smoke reduction due to lowering combustion temperatures and avoiding local overrich regions in the mixtures respectively.

Fuel Design Concept for Low Emission in Engine Systems 4th Report: Effect of Spray Characteristics of Mixed Fuel on Exhaust Concentrations in Diesel Engine

In this study, the novel fuel design concept has been proposed in order to realize the low emission and combustion control in engine systems. In this fuel design concept, the mixed fuels with a high volatility fuel (gasoline or gaseous fuel components) and a low volatility fuel (gas oil or fuel oil components) are used in order to improve the spray characteristics by flash boiling. In our previous papers on this study, the fundamental characteristics of spray and its combustion of mixed fuel were reported. In this paper, heat release and exhaust emission (smoke, NOx and THC) characteristics of single cylinder diesel engine operated with the mixed fuels were investigated under each load. The exhaust performance of diesel engine could be improved using mixed fuel, because fuel properties and spray characteristics were controlled by changing mixing fraction of the mixed fuel. Moreover, in this exhaust gas concentration measurement, initial fuel temperature was employed for experimental parameter in order to control flash boiling process in mixed fuel spray, for flash boiling can be easily occurred by increasing initial fuel temperature. As a preliminary investigation of the flash boiling effect, the spray experiment for mixed fuel was conducted using constant volume vessel. As a result, it was confirmed that flash boiling had the potential of drastic reduction of smoke emission since flash boiling improved the atomization and vaporization of mixed fuel spray with rapid fuel-air mixing.

A Study on NOx Emission Characteristics When Using Biomass-derived Diesel Alternative Fuels

This study evaluates nitrogen oxides (NOx) emission characteristics with the heavy-duty diesel engine when using various fatty acid methyl esters (FAMEs) and hydrocarbon fuels on the assumption of biomass-derived diesel alternative fuels. The relationship between NOx emission characteristics and fuel properties of these fuels is then discussed and effectiveness of paraffinic hydrocarbon fuel is indicated. In the case of paraffinic hydrocarbon fuel, NOx emission could be suppressed to be increased due to the almost same lower heating value per unit volume and its high H/C ratio compared with those of conventional diesel fuel.

Comparative Measurement of Nano-Particulates in Diesel Engine Exhaust Gas by Laser-Induced Incandescence (LII) and Scanning Mobility Particle Sizer (SMPS)

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (Lll) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the Lll and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both Lll and SMPS. In the present study, the size distributions of PM from Dl diesel engine are measured by both Lll and SMPS simultaneously. In addition, PM mass emission is measured gravimetrically through a dilution tunnel and is separated into SOF and ISOF. The effects of EGR rate and engine load on the results of these particulate measurements are investigated. The different trends in the characteristics of PM emission are shown in each measurement methods for PM. The difference of detailed characteristics between Lll and SMPS are illustrated by comparing the measurement results for the particulates. Finally, the problems associated with the measurements using each method are considered and some recommendations have been given for accurate measurement of nanoparticles.

Bench test of minimum time autonomous driving for electric vehicle based on optimization of velocity profile considering energy constraint

Recently, Intelligent Transport Systems (ITS) technology have been intensively studied to solve environmental and energy problems by improving traffic flow. Along with the development of ITS and autonomous driving technologies, vehicle velocity control has to be considered for energy efficiency. In this paper, a minimum time autonomous driving (MTAD) system, which minimizes the traveling time considering energy constraint for an electric vehicle (EV), is proposed. The proposed method minimizes the traveling time by optimizing the velocity profile and front and rear driving-braking force distribution. The effectiveness of the proposed method is verified by simulations and bench tests.

Field and bench test evaluation of range extension control system for electric vehicles based on front and rear driving-braking force distributions

Electric vehicles (EVs) have a disadvantage in that the cruising distance per charge is short. This paper proposes a model-based range extension control system (RECS) for EVs. The proposed system optimizes the front and rear driving-braking force distributions by considering the slip ratio of the wheels and the motor loss. The optimal distribution depends solely on the vehicle acceleration and velocity. Therefore, this system is effective not only at constant speeds but also in acceleration and deceleration modes. Bench tests were conducted for more precise evaluation and to realize experimental results with high reproducibility. The effectiveness of the proposed system was verified through field and bench tests.

Range extension autonomous driving for electric vehicles based on optimal velocity trajectory and driving braking force distribution considering road gradient information

Electric Vehicles (EVs) are deemed as an appealing and practical solution for environmental and energy problems. The mileage per charge of EVs, however, is shorter than the mileage of Internal Combustion Engine Vehicles (ICEVs). In this paper, Range Extension Autonomous Driving (READ) system considering road gradient information is proposed. The proposed system optimizes the velocity trajectory and the driving-braking force distribution ratio for autonomous driving. The authors carried out simulations and bench tests that prove the effectiveness of the proposal in terms of mileage per charge.

Modeling of Evaporation Process of Multicomponent Fuel Spray

Original KIVA code cannot take account for the spray and combustion processes of multicomponent fuels. Therefore, it is necessary to produce the sub-models for multicomponent fuel using KIVA code. In this study, the modeling of detailed physical properties and evaporation process for multicomponent fuel was conducted. In addition, the effects of fuel composition in multicomponent fuel on vapor distribution, spray tip penetration, vapor mass and evaporation rate, and sauter mean diameter were numerically investigated by using KIVA 3 V code with this multicomponent fuel spray model. From the numerical results, the spray characteristics of multicomponent fuel varied with a change in mixing fraction in multicomponent fuel. Especially, the evaporation of multicomponent fuel was not necessarily improved, even if much amount of high volatility fuel was mixed in the multicomponent fuel.