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Technical Paper

Visualization of Fuel-Air Mixing Processes in a Small D.I. Diesel Engine Using the Liquid injection Technique

Simplified visualization of the fuel spray developing process in a small D.I. diesel engine was made by the liquid injection technique. In this technique, a liquid fuel was injected into another liquid to simulate injection into a high pressure gaseous atmosphere. For obtaining spray characteristics in the liquid similar to a diesel spray in a high-pressure gaseous atmosphere, the similarity principles based on the Reynolds number of the fuel flow at a nozzle hole and empirical equations of the spray penetration including the breakup length were introduced in this study. Especially, the injector was newly designed for the liquid injection technique based on these similarity principles. The behavior of the spray in a swirling flow was investigated. The spray with different breakup length shows different behavior in the same swirling flow.
Technical Paper

Vapor/Liquid Behaviors in Split-Injection D.I. Diesel Sprays in a 2-D Model Combustion Chamber

Some experimental investigations have shown that the trade-off curve of NOx vs. particulate of a D.I. diesel engine with split-injection strategies can be shifted closer to the origin than those with a single-pulse injection, thus reducing both particulate and NOx emissions significantly. It is clear that the injection mass ratios and the dwell(s) between injection pulses have significant effects on the combustion and emissions formation processes in the D.I. diesel engine. However, how and why these parameters significantly affect the engine performances remains unexplained. The effects of both injection mass ratios and dwell between injections on vapor/liquid distributions in the split-injection diesel sprays impinging on a flat wall have been examined in our previous work.
Technical Paper

Utilizing FAME as a Cetane Number Improver for a Light-duty Diesel Engine

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.
Technical Paper

Unsteady Three-Dimensional Computational Experiments of the Single-Point Auto-Ignition Engine Based on Semispherical Supermulti-Jets Colliding with Pulse for Automobiles

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.
Technical Paper

Two-Dimensional Measurements of the Fuel Vapor Concentration in the Combustion Chamber of a SI Engine with Laser Rayleigh Scattering

An experimental study was made of the two-dimensional distributions of the fuel vapor concentration simulated by Freon-12 in the combustion chamber of a SI engine. Laser Rayleigh scattering was applied for this remote, nonintrusive and highly space- and time-resolved measurement. The original engine was modified to introduce YAG laser-induced sheet light into the combustion chamber and the scattered light was captured by a CCD camera fitted with a gated double-microchannel plate image intensifier. The results showed that the fuel vapor concentration was highly heterogeneous during the intake stroke and the inhomogeneity decreased in the compression stroke. But, even at the end of the compression stroke, a number of small lumps of inhomogeneous mixture still existed randomly in the engine combustion chamber, which is assumed to cause the heterogeneity of the mixture strength field at the spark discharge.
Technical Paper

Total In-Cylinder Sampling Experiment on Emission Formation Processes in a D.I. Diesel Engine

An experimental study on emission formation processes, such as these of nitric oxide, particulate and total hydrocarbon in a small direct injection (D.I.) diesel engine was carried out by using a newly developed total in-cylinder sampling technique. The sampling method consisted of rapidly opening a blowdown valve attached to the bottom of the piston bowl, and quickly transferring most of the in-cylinder contents into a large sampling chamber below the piston. No modification of the intake and exhaust ports in a cylinder head was required for the installation of the blowdown apparatus. The sampling experiment gave a history of spatially-averaged emission concentrations in the cylinder. The effects of several engine variables, such as the length-to-diameter ratio of the nozzle hole, the ratio of the piston bowl diameter to the cylinder bore and the intake swirl ratio, on the emission formation processes were investigated.
Technical Paper

Three-Dimensional Spray Distributions in a Direct Injection Diesel Engine

Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditions (pressure and density) at an ambient temperature. The diesel fuel was delivered from a Bosch-type injection pump to a single-hole nozzle, the hole being drilled in the same direction as the original five-hole nozzle. The fuel was injected into a high-pressure bomb in which an engine combustion chamber, composed of a piston, a cylinder head and a cylinder liner, was installed. Distributions of the spray impinged on the simulated combustion chamber were observed from various directions while changing some of the experimental parameters, such as combustion chamber shape, nozzle projection and top-clearance. High-speed photography was used in the constant volume bomb to examine the effect of these parameters on the spray distributions.
Technical Paper

The Control of Diesel Emissions by Supercharging and Varying Fuel-injection Parameters

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.
Technical Paper

Swirl Measurements and Modeling in Direct Injection Diesel Engines

A simple, but useful method is described for predicting the swirl speed during the compression process in a direct injection diesel engine. The method is based on the idea of dividing the combustion chamber into two volumetric regions and computing the variation of the angular momentum in each region. Laser doppler velocimeter measurements in a motored engine proved the validity of the idea that the volume in the combustion chamber should be treated as two regions, that is, the cylindrical volume inside the piston-cavity radius, and the annular volume outside the piston-cavity radius. Distributions of tangential velocities were measured for different conditions, including the intake port configuration, the piston cavity shape, the compression ratio and the engine speed. These results were integrated in the two regions and provided the measured “two volume-regions” swirl ratio. At the same time, the computation was carried out for the same experimental conditions.
Technical Paper

Study on Design and Performance Prediction Methods for Miniaturized Stirling Engine

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.
Technical Paper

Study on Burning Velocity of LPG Fuel in a Constant Volume Combustion Chamber and an SI Engine

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).
Technical Paper

Spray and Mixture Properties of Hole-Type Injector for D. I. Gasoline Engine-Comparison of Experiment and CFD Simulation-

An experimental and numerical study was conducted on the spray and mixture properties of a hole-type injector for direct injection (D. I.) gasoline engines. The Laser Absorption Scattering (LAS) technique was adopted to simultaneously measure the spatial concentration distributions and the mass of the liquid and vapor phases in the fuel spray injected into a high-pressure and high-temperature constant volume vessel. The experimental results were compared to the numerical calculation results using three-dimensional CFD and the multi-objective optimization. In the numerical simulation, the design variable of the spray model was optimized by choosing spray tip penetration, and mass of liquid and vapor phases as objective functions.
Technical Paper

Spray and Flame Behaviors of Ethanol-Gasoline Blend Injected by Hole-Type Nozzle for DISI Engine

Different ethanol-gasoline blended fuels, namely the E0 (100% gasoline), E85 (85% ethanol and 15% gasoline mixed in volume basis) and E100 (100% ethanol) were injected by a valve-covered-orifice (VCO) hole-type nozzle in a condition simulating the near top dead center (TDC). Two typical injection pressures of 10 and 20MPa were adopted to clarify the spray and flame behaviors. The correlation of the upstream unburned fuel and the flame propagation was analyzed by the high-speed imaging of shadowgraph. Moreover, the effects of ignition timing and location on the flame propagation were discussed based on the imaging of OH* chemiluminescence.
Technical Paper

Spray and Evaporation Characteristics of Multi-Hole Injector for DISI Engines - Effect of Diverging Angle Between Neighboring Holes

Experimental and computational studies were carried out to characterize the spray development and evaporation processes of multi-hole injector for direct injection spark ignition (DISI) engines. The main injector parameter to be investigated in this study is a diverging angle between neighboring two holes. In the experimental study, the influence of the diverging angle on evaporation process of fuel spray from two-hole injector was investigated using Laser Absorption Scattering (LAS) measurement. Smaller diverging angle causes larger spray tip penetration because the momentum of the spray from one hole emphasizes another, when two spray merge to one. Moreover, spray tip penetration decreases at certain diverging angle due to the negative pressure region between two sprays. Mechanisms behind the above spray behaviors were discussed using the detailed information on the spray and ambient gas flow fields obtained by the three dimensional computational fluid dynamics (CFD).
Technical Paper

Spray Characteristics of Group-hole Nozzle for D.I. Diesel Engine

Reduction of orifice diameter of nozzle is advantageous to the fuel atomization in a D.I. diesel engine. However, the diameter reduction is usually accompanied with decrease of spray tip penetration, thus worsening fuel spatial-distribution and fuel-air mixing. In this paper, a group-hole nozzle concept was proposed to solve the problem resulting from minimization of orifice diameter. Compared to the conventional multi-hole nozzle, group-hole nozzle has a series group of orifices, and each group consists of two micro-orifices with a small spatial interval and small angle. For examining the characteristics of the spray injected by the group-hole nozzle, the ultraviolet-visible laser absorption-scattering (LAS) imaging technique was adopted to determine vapor concentration and droplets density as well as other spray characteristics such as spray angle and penetration of both vapor and liquid phases.
Technical Paper

Split Injection Spray Development, Mixture Formation, and Combustion Processes in a Diesel Engine Piston Cavity: Rig Test and Real Engine Results

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.
Journal Article

Small Injection Amount Fuel Spray Characteristics Injected by Hole-Type Nozzle for D.I. Diesel Engine

Spray characteristics under very small injection amount injected by the hole-type nozzle for a D.I. Diesel engine were investigated using the spray test rig consisting a high-pressure and high-temperature constant volume vessel with optical accesses and a common rail injection system. The Laser Absorption Scattering (LAS) technique was used to visualize the liquid and vapor phase distributions in the evaporating spray. In the very small injection amount condition of the evaporating and free (no wall impingement) spray, the both spray tip penetration and spray angle are larger than those of the non-evaporating free spray. This tendency contradicts the previous observation of the diesel spray with large injection amount and the quasi steady state momentum theory. In the case of the spray impinging on a 2-dimensional piston cavity wall, the spray tip penetration of the evaporating spray is larger than that of the non-evaporating spray.
Technical Paper

Simultaneous Flow Field Measurement of D.I. Gasoline Spray and Entrained Ambient Air by LIF-PIV Technique

The spray and the entrained ambient air motions produced by a swirl-type D.I. gasoline injector were simultaneously measured by combining the laser induced fluorescence (LIF) and the particle image velocimetry (PIV) techniques. For the simultaneous measurement of the spray and the ambient air velocities, the succeeding two image pairs of the fuel spray and the ambient air tracer particles were captured by using a Nd:YAG laser light sheet (wave length: 532 nm) and two high-resolution CCD cameras. The light emitted from the fluorescent tracer clouds was discriminated from the light scattered from the droplets in the fuel spray by an optical low-pass filter (>560 nm), and the Mie scattering signals from the spray particles were screened by a band-pass filter ranging from 520 to 545 nm. The spray and the tracer particle images were analyzed by the double frame cross-correlation PIV technique to obtain the droplets and ambient air velocity distributions.
Technical Paper

Simulation Study of Effects of Injection Rate Profile and Air Entrainment Characteristics on D.I. Diesel Combustion

A calculative investigation was performed in order to examine the effects of injection rate profile and air entrainment characteristics on exhaust emission using a phenomenological spray combustion model. The calculations were made of an engine with a bore of 114 mm and a stroke of 130 min while changing the injection rate profile and the air entrainment characteristics. As a result of the calculations, effective measures were found for simultaneous reduction of NOx and smoke emissions.
Technical Paper

Simulating Exhaust Emissions Characteristics and Their Improvements in a Glow-Assisted DI Methanol Engine Using Combustion Models Combined with Detailed Kinetics

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.