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As the petroleum depletion, some of this demand will probably have to be met by increasing the production of diesel fuels from heavy oil or unconventional oil in the near future. Such fuels may inevitably have a lower cetane number (CN) with a higher concentration of aromatic components. The objective of the present research is to identify the effects of a typical biodiesel fuel as a CN improver for a light-duty diesel engine for passenger cars. Our previous study indicates that methyl oleate (MO), which is an oxygenated fuel representative of major constituents of many biodiesel types, can reduce soot and NOx emissions simultaneously by optimizing performance under exhaust gas recirculation (EGR) when used as a diesel fuel additive. In addition, it was found that MO tends to reduce the ignition delay. We employed a 2.2 L passenger car DI diesel engine complying with the Euro 4 emissions regulation.

Supercomputer simulations substantiate a high potential of the new compressive combustion principle based on supermulti-jets colliding with pulse, which was previously proposed by us and can maintain high compression ratio for various air-fuel ratios. An original governing equation extended from the stochastic Navier-Stokes equation lying between the Boltzmann and Langevin equations is proposed and the numerical methodology based on the multi-level formulation proposed previously by us is included. For capturing instability phenomena, this approach is better than direct numerical simulation (DNS) and large eddy simulation (LES). A simple two-step chemical reaction model modified for gasoline is used. A small engine having a semispherical distribution of seventeen jets pulsed is examined here. Pulse can be generated by a rotary plate valve, while a piston of a short stroke of about 65mm is also included.

A study has been made of an automotive direct injection diesel engine designed to reduce exhaust emissions, particularly NOx and particulates, without performance deterioration. Special emphasis has been placed on air-fuel mixing conditions controlled by the fuel injection rate, the intake swirl ratio, and the intake boost pressure. By means of increasing the injection rate, ignition delay can be shortened enough to improve particulate emissions at retarded injection timings. Enhancing the intake swirl velocity contributes to the reduction of soot emission in spite of the deterioration of NOx emission. Supercharging can favorably enhance diffusion combustion resulting in improved fuel economy for retarded injection timings and reduced emissions. As a result, a good compromise can be achieved between fuel economy and exhaust emissions by increasing the injection rate along with retarding the injection timing. Supercharging was found to be more favorable than swirl enhancement.

This paper shows a design and performance prediction methods for a miniaturized Stirling engine, in order to develop a small portable generator set. First, a 100 W class Stirling engine is designed and manufactured. In order to miniaturize the engine, unique type heat exchangers were applied. A regenerator was located in a displacer piston. For a piston drive mechanism, a Scotch-yoke mechanism which was useful to realize the small-size engine without any lubricating device, was adopted. Next, an analysis model for the miniaturized engine is developed to improve the engine performance efficiently. The pressure in the working space is analyzed by an isothermal analysis which takes into account a gas leakage through a piston ring and pressure loss in the heat exchangers. To estimate a shaft power, the mechanical loss and the buffer loss, which is caused by a pressure change in a crank case are considered on the analysis model.

Compared with petroleum fuel, liquefied petroleum gas (LPG) demonstrates advantages in low CO₂ emission. This is because of propane (C₃H₈), n-butane (n-C₄H₁₀) and i-butane (i-C₄H₁₀), which are the main components of LPG, making H/C ratio higher. In addition, LPG is suitable for high efficient operation of a spark ignition (SI) engine due to its higher research octane number (RON). Because of these advantages, that is, diversity of energy source and reduction of CO₂, in the past several years, LPG vehicles have widely been used as the alternate gasoline vehicles all over the world. Consequently, it is absolutely essential for the performance increase in LPG vehicles to comprehend combustion characteristics of LPG. In this study, the differences of laminar burning velocity between C₃H₈, n-C4H10, i-C₄H₁₀ and regular gasoline were evaluated experimentally with the use of a constant volume combustion chamber (CVCC).

The objectives of this study are to investigate the effects of premixed charge compression ignition (PCCI) strategies with split injection on soot emission characteristics. The split injection conditions included three injection intervals (1.1 ms, 1.3 ms, and 1.5 ms) and three injection quantity fraction ratios (Q1/Q2 = 10.0/14.6 mm3/st, 15.2/9.4 mm3/st, and 20.0/4.6 mm3/st). The results in real engine tests showed that shorter injection intervals, and the 1st injection quantity contributes to reduced soot emissions. A rig test with high-pressure and high-temperature constant-volume vessel (CVV) and a two-dimensional (2D) model piston cavity were used to determine correlations between injection conditions and soot emissions. During the rig test, fuel was injected into the CVV by a single-hole nozzle under split injection strategies. The injection strategies include the same injection intervals and quantity fraction ratios as in the real engine test.

An experimental and numerical study has been conducted on the emission and reduction of HCHO (formaldehyde) and other pollutants formed in the cylinder of a direct-injection diesel engine fueled by methanol. Engine tests were performed under a variety of intake conditions including throttling, heating, and EGR (exhaust gas recirculation) for the purpose of improving these emissions by changing gas compositions and combustion temperatures in the cylinder. Moreover, a detailed kinetics model was developed and applied to methanol combustion to investigate HCHO formation and the reduction mechanism influenced by associated elementary reactions and in-cylinder mixing.

A numerical model has been developed to predict the formation of NOx and formaldehyde in the combustion and post-combustion zones of a methanol DI engine. For this purpose, a methanol-air mixture model combined with a full kinetics model has been introduced, taking into account 39 species with their 157 related elementary reactions. Through these kinetic simulations, a concept is proposed for optimizing methanol combustion and reducing exhaust emissions.

This paper proposes a new compressive combustion principle for an inexpensive, lightweight, and relatively quiet engine reactor that has the potential to achieve incredible thermal efficiency over 60% even for small engines having strokes shorter than 100mm, whereas eco-friendly gasoline engines for today's automobiles use less than 35% of the supplied energy for work on average. This level of efficiency can be achieved with colliding supermulti-jets that create air insulation to encase burned gas around the chamber center, thereby avoiding contact with the chamber walls, including the piston. Emphasis is also placed on the fact that higher compression results in less combustion noise because of the encasing effect. We will first show that numerical computations done for two jets colliding in line quantitatively agree with shock-tube experiment and theoretical value based on compressible fluid mechanics.

The objective of the present study is to analyze soot formation in diesel engine combustion by using multi-dimensional combustion simulations with a parallelized explicit ODE solver. Parallelized CHEMEQ2 was used to perform detailed chemical kinetics in KIVA-4 code. CHEMEQ2 is an explicit stiff ODE solver developed by Mott et al. which is known to be faster than traditional implicit ODE solvers, e.g., DVODE. In the present study, about eight times faster computation was achieved with CHEMEQ2 compared to DVODE when using a single thread. Further, by parallelizing CHEMEQ2 using OpenMP, the simulations could be run not only on calculation servers but also on desktop machines. The computation time decreases with the number of threads used. The parallelized CHEMEQ2 enabled combustion and emission characteristics, including detailed soot formation processes, to be predicted using KIVA-4 code with detailed chemical kinetics without the need for reducing the reaction mechanism.

To facilitate research and development of diesel engines, the universal numerical code for predicting diesel combustion has been favored for the past decade. In this paper, the finite-rate elementary chemical reactions, sometimes called the detailed chemical reactions, are introduced into the KIVA-3V code through the use of the Partially Stirred Reactor (PaSR) model with the KH-RT break-up, modified collision and velocity interpolation models. Outcomes were such that the predicted pressure histories have favorable agreements with the measurements of single and double injection cases in the diesel engine for use in passenger cars. Thus, it is demonstrated that the present model will be a useful tool for predicting ignition and combustion characteristics encountered in the cylinder.

An author's previous studies addressed a combustion system which reduces emissions, noise, and fuel consumption by using PCCI with the split injection of fuel. This concept relies on the premixed combustion of the first injected fuel and accelerated oxidation by the second injected fuel. Although this combustion system requires the optimization of the timing of the second injection, the details of how noise and emissions are reduced have not been elucidated. In this paper, the authors explain the mechanism whereby emissions and noise are reduced by the second injection. In-cylinder visualizations and numerical simulations both showed an increase in smoke and CO as the second injection timing was advanced, as induced by the inhibited oxidation of the rich flame. When the second injection timing is excessively retarded, the amount of soot forming around the near-nozzle increased.

This paper describes the development of a High Speed Calculation Diesel Combustion Model that predicts combustion-related behaviors of diesel engines from passenger cars. Its output is dependent on the engine's operating parameters and on input from on-board pressure and temperature sensors. The model was found to be capable of predicting the engine's in-cylinder pressure, rate of heat release, and NOx emissions with a high degree of accuracy under a wide range of operating conditions at a reasonable computational cost. The construction of this model represents an important preliminary step towards the development of an integrated Model Based Control system for controlling combustion in diesel engines used in passenger cars.

Model based control design is an important method for optimizing engine operating conditions so as to simultaneously improve engines' thermal efficiency and emission profiles. Modeling of intake system that includes an intake throttle valve, an EGR valve and a variable geometry turbocharger was constructed based on conservation laws combined with maps. Calculated results were examined the predictive accuracy of fresh charge mass flow, EGR rate and boost pressure.

Multi-cylinder hydrogen-absorbing alloy tanks for fuel cell vehicles have 10 to 40 metallic cylinders that are bundled and filled with hydrogen-absorbing alloy. In this system, the cylinders themselves act as a heat exchanger and the working pressure is lowered to 10 to 20 MPa compared with high-pressure MH tanks. Moreover, both heat conduction and mass reduction can be achieved by reducing the wall thickness of the cylinders. A model verification experiment was conducted using a one-quarter-scale prototype of a full size tank, and a conduction simulation model verified in the experiment was used to predict the performance of the full size tank. Results showed that it is possible to fill the tank with hydrogen to 80% of its capacity in a five-minute filling time, although issues related to heat conductivity performance require improvement. Accordingly, it may be possible to adopt this tank as part of a system if the storage amount of the hydrogen-absorbing alloy can be increased.

We proposed a new compressive combustion principle for an inexpensive and relatively quiet engine reactor that has the potential to achieve incredible thermal efficiency. The high efficiency can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center. We developed a small prototype engine system for gasoline, which has a strongly-asymmetric double piston and the supermulti-jets colliding with pulse. In this report, we will show combustion experimental results at startup and at steady state operation. We obtained exhaust temperature over 100 degree Celsius and pressure data, which imply auto-ignition occurrence of gasoline.

Primary work is to investigate premixed laminar flame propagation in a constant volume chamber of iso-octane/air combustion. Experimental and numerical results are investigated by comparing flame front displacements under lean to rich conditions. As the laminar flame depends on equivalence ratio, temperature, and pressure conditions, it is a main property for chemical reaction mechanism validation. Firstly, one-dimensional laminar flame burning velocities are predicted in order to validate a reduced chemical reaction mechanism. A set of laminar burning velocities with pressure, temperature, and mixture equivalence ratio dependences are combined into a 3D-CFD calculation to compare the predicted flame front displacements with that of experiments. It is found that the reaction mechanism is well validated under the coupled 1D-3D combustion calculations. Next, lean experiments are operated in a SI engine by boosting intake pressure to maintain high efficiency without output power penalty.

The use of biomass fuels for vehicles has been a focus of attention all over the world in terms of prevention of global warming, effective utilization of resources and local revitalization. For the purpose of beneficial use of unused biomass resources, the movement of the use of bioethanol and biodiesel made from them has spread in Japan. In Japan, biodiesel is mainly made from waste cooking oil collected by local communities or governments, and in terms of local production for local consumption, it is used as neat fuel (100% biofuel) or mixed with diesel fuel in high concentration for the vehicles. On the other hand, extremely low emission level must be kept for not only gasoline vehicles but also diesel vehicles in the post new long-term regulation implemented from 2009 in Japan.

Vibration has been the most objectable problem that inevitably occurs in high speed multi-cylinder diesel engines. The torsional vibration appearing at the crankshaft of the engine is the major source of the engine vibration. A torsional damper, being attached at the end of the crankshaft, has been widely used to reduce the torsional vibration. For this purpose, various kinds of damper as examplified by a double-mass type and a viscous-rubber type have been subject to many investigations during these twenty years. However, less attention has been paid on dynamic characteristics of a shear-type single mass rubber damper in spite of its potential. Thus, the purpose of this study has been directed to establish the concept for designing a best tuned torsional rubber damper. In this work, rubber geometry is considered as one of the most essential factors influencing on dynamic characteristics of the rubber damper.

In our previous reports based on computational experiments and fluid dynamic theory, we proposed a new compressive combustion principle for an inexpensive, lightweight, and relatively quiet engine reactor that has the potential to achieve incredible thermal efficiency over 60% even for small combustion chambers having less than 100 cc. This level of efficiency can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center, thereby avoiding contact with the chamber walls, including the piston. We originally developed an actual prototype engine system for gasoline. The engine has a strongly-asymmetric double piston and the supermulti-jets colliding with pulse, although there are no poppet valves. The number of jets pulsed for intake and exhaust is eight, while both of bore and stroke are about 40mm.