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Technical Paper

Generation of Robust and Well-Atomized Swirl Spray

2007-07-23
2007-01-1852
The spray characteristics of a swirl injector for direct-injection spark-ignition (DISI) engines were investigated for the generation of robust and well-atomized swirl spray. A highly-inclined tapered nozzle is applied as a test nozzle and the spray characteristics are compared with conventional nozzle and L-step nozzle. When the taper angle is 70°, an opened hollow cone spray is formed. This spray does not collapse with increasing fuel temperature and back pressure conditions. However, the taper angle should be optimized to avoid forming a locally rich area and to increase the spray volume. The droplet size of 70° tapered nozzle spray shows a value similar to that of the original swirl spray in the horizontal mainstream while it shows an increased value in the vertical mainstream. The deteriorated atomization characteristics of the tapered nozzle spray are improved by applying high fuel temperature injection without causing spray collapse.
Technical Paper

Two-stage Fuel Direct Injection in a Diesel Fuelled HCCI Engine

2007-07-23
2007-01-1880
Two-stage fuel direct injection (DI) has the potential to expand the operating region and control the auto-ignition timing in a Diesel fuelled homogeneous charge compression ignition (HCCI) engine. In this work, to investigate the dual-injection HCCI combustion, a stochastic reactor model, based on a probability density function (PDF) approach, is utilized. A new wall-impingement sub-model is incorporated into the stochastic spray model for direct injection. The model is then validated against measurements for combustion parameters and emissions carried out on a four stroke HCCI engine. The initial results of our numerical simulation reveal that the two-stage injection is capable of triggering the charge ignition on account of locally rich fuel parcels under certain operating conditions, and consequently extending the HCCI operating range.
Technical Paper

Load Limits with Fuel Effects of a Premixed Diesel Combustion Mode

2009-06-15
2009-01-1972
Premixed diesel combustion is intended to supplant conventional combustion in the light to mid load range. This paper demonstrates the operating load limits, limiting criteria, and load-based emissions behavior of a direct-injection, diesel-fueled, premixed combustion mode across a range of test fuels. Testing was conducted on a modern single-cylinder engine fueled with a range of ultra-low sulfur fuels with cetane number ranging from 42 to 53. Operating limits were defined on the basis of emissions, noise, and combustion stability. The emissions behavior and operating limits of the tested premixed combustion mode are independent of fuel cetane number. Combustion stability, along with CO and HC emissions levels, dictate the light load limit. The high load limit is solely dictated by equivalence ratio: high PM, CO, and HC emissions result as overall equivalence ratio approaches stoichiometric.
Technical Paper

Effect of Multiple Injection Strategies on Emission and Combustion Characteristics in a Single Cylinder Direct-Injection Optical Engine

2009-04-20
2009-01-1354
The effect of multiple injections in a heavy-duty diesel engine was investigated by focusing on single-pilot injection and double-pilot injection strategies with a wide injection timing range, various injection quantity ratios, and various dwell times. Combustion characteristics were studied through flame visualization and heat release analyses as well as emissions tests. Single-pilot injection resulted in a dramatic reduction in nitrogen oxide and smoke emissions when the injection timing was advanced over 40° CA before the start of injection (BSOI) due to combustion with partially premixed charge compression ignition. A brown-colored flame area, which indicates a very fuel-rich mixture region, was rarely detected when more fuel was injected during single-pilot injection. However, hydrocarbon emission increased up to intolerable levels because fuel wetting on the cylinder wall increased.
Technical Paper

The Effect of Injection Location of DME and LPG in a Dual Fuel HCCI Engine

2009-06-15
2009-01-1847
Dimethyl ether (DME) as a high cetane number fuel and liquefied petroleum gas (LPG) as a high octane number fuel were supplied together to evaluate the controllability of combustion phase and improvement of power and exhaust emission in homogeneous charge compression ignition (HCCI) engine. Each fuel was injected at the intake port and in the cylinder separately during the same cycle, i.e., DME in the cylinder and LPG at the intake port, or vice versa. Direct injection timing was varied from 200 to 340 crank angle degree (CAD) while port injection timing was fixed at 20 CAD. In general, the experimental results showed that DME direct injection with LPG port injection was the better way to increase the IMEP and reduce emissions. The direct injection timing of high cetane number fuel was important to control the auto-ignition timing because the auto-ignition was occurred at proper area, where the air and high cetane number fuel were well mixed.
Technical Paper

Development of an In-Cylinder Heat Transfer Model with Compressibility Effects on Turbulent Prandtl Number, Eddy Viscosity Ratio and Kinematic Viscosity Variation

2009-04-20
2009-01-0702
In-cylinder heat transfer has strong effects on engine performance and emissions and heat transfer modeling is closely related to the physics of the thermal boundary layer, especially the effects of conductivity and Prandtl number inside the thermal boundary layer. Compressibility effects on the thermal boundary layer are important issues in multi-dimensional in-cylinder heat transfer modeling. Nevertheless, the compressibility effects on kinematic viscosity and the variation of turbulent Prandtl number and eddy viscosity ratio have not been thoroughly investigated. In this study, an in-cylinder heat transfer model is developed by introducing compressibility effects on turbulent Prandtl number, eddy viscosity ratio and kinematic viscosity variation with a power-law approximation. This new heat transfer model is implemented to a spark-ignition engine with a coherent flamelet turbulent combustion model and the RNG k- turbulence model.
Technical Paper

The Feasibility of an Alumina-Based Lean NOx Trap (LNT) for Diesel and HCCI Applications

2008-04-14
2008-01-0451
An alumina-based LNT is being developed through laboratory studies, for diesel vehicle applications. This LNT provides high NOx conversion efficiency at low temperature (150 to 350°C, especially below 200°C), which is very important for the exhaust-gas after-treatment of diesel passenger vehicles. Addition of 2 to 4 wt% of alkaline-earth metal oxide or other metal oxides to the alumina LNT formulation improves NOx reduction activity at the high end of its active temperature window. More significantly, the alumina-based LNT can undergo the de-SOx process (the process of removing sulfur from the catalytic surfaces) very efficiently: within 1 minute at the relatively low temperature of 500 to 650°C under slightly rich conditions (λ = 0.98 to 0.987). Such a mild de-SOx process imposes minimal thermal exposure, causing almost no thermal damage to the LNT, and helps minimize the associated fuel penalty.
Technical Paper

Effect of Injection Parameters on the Combustion and Emission Characteristics in a Compression Ignition Engine Fuelled with Waste Cooking Oil Biodiesel

2013-10-14
2013-01-2662
An experimental study was conducted to investigate the impact of injection parameters on the combustion and emission characteristics in a compression ignition engine fuelled with neat waste cooking oil (WCO) biodiesel. A single-cylinder diesel engine equipped with common-rail system was used in this research. The test was performed over two engine loads at an engine speed of 800 r/min. Injection timing was varied from −25 to 0 crank angle degree (CAD) after top dead center (aTDC) at two different injection pressures (80 and 160 MPa). Based on in-cylinder pressure, heat release rate was calculated to analyze the combustion characteristics. Carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) and smoke were measured to examine the emission characteristics. The results showed that the indicated specific fuel consumption (ISFC) of WCO biodiesel was higher than that of diesel. The ISFC was increased as the injection timing was advanced and injection pressure was increased.
Technical Paper

Assessment of Soot Particles in an Exhaust Gas for Low Temperature Diesel Combustion with High EGR in a Heavy Duty Compression Ignition Engine

2013-10-14
2013-01-2572
The characteristics of soot particles in an exhaust gas for low temperature diesel combustion (LTC) compared with conventional combustion in a compression ignition engine were experimentally investigated by the elemental and thermogravimetric analysis (TGA). Morphology of soot particles was also studied by the transmission electron microscopy (TEM). From the result of the TGA, the water can be evaporated until about 150°C for both combustion regimes. The soot particles for LTC contained more volatile hydrocarbons, which can be easily evaporated from 200°C to 420°C compared with conventional diesel combustion. The soot oxidation for conventional combustion occurs up to 600°C, on the other hand the particles for LTC is oxidized below 520°C. Elemental analysis showed higher oxygen weight fraction resulted from the oxygenated hydrocarbon for the soot particles in LTC. TEM has shown primary particles to be in a diameter range of 20 to 50 nm for conventional diesel combustion.
Technical Paper

Spray and Combustion Visualization of Gasoline and Diesel under Different Ambient Conditions in a Constant Volume Chamber

2013-10-14
2013-01-2547
Spray and combustion of gasoline and diesel were visualized under different ambient conditions in terms of pressure, temperature and density in a constant volume chamber. Three different ambient conditions were selected to simulate the three combustion regimes of homogeneous charge compression ignition, premixed charge compression ignition and conventional combustion. Ambient density was varied from 3.74 to 23.39 kg/m3. Ambient temperature at the spray injection were controlled to the range from 474 to 925 K. Intake oxygen concentration was also modulated from 15 % to 21 % in order to investigate the effects of intake oxygen concentrations on combustion characteristics. The injection pressure of gasoline and diesel were modulated from 50 to 150 MPa to analyze the effect of injection pressure on the spray development and combustion characteristics. Liquid penetration length and vapor penetration length were measured based on the methods of Mie-scattering and Schileren, respectively.
Journal Article

Characteristics of Turbocharger with TiAl Turbine Wheel in a Downsizing GDI Engine

2013-10-14
2013-01-2499
Steady and transient tests in a downsizing Gasoline Direct Injection (GDI) in-line 4 cylinders 2.0 liter engine were carried out to investigate characteristics of turbocharger with Titanium aluminide (TiAl) turbine wheel. The density of TiAl material is lower than Inconel 718 (Inconel) which is raw material for conventional turbine wheel. The objective of this study was to investigate the effect of light rotational inertia of turbine wheel on engine performance. Performance of TiAl turbine wheel turbocharger itself was also compared to that of Inconel turbine wheel turbocharger. Except for the turbine wheels, all experimental conditions were matched to be the same load and engine speed conditions. The compressor total-to-total pressure ratio of TiAl turbocharger was higher under part load condition due to higher turbocharger speed of TiAl turbocharger, which was led by lower rotational inertia of TiAl turbine wheel, while the engine performance was not much improved.
Technical Paper

Operating Characteristics of DME-Gasoline Dual-fuel in a Compression Ignition Engine at the Low Load Condition

2013-03-25
2013-01-0049
Combustion and emission characteristics were investigated in a compression ignition engine with dual-fuel strategy using dimethyl ether (DME) and gasoline. Experiments were performed at the low load condition corresponding to indicated mean effective pressure of 0.45 MPa. DME was directly injected into the cylinder and gasoline was injected into the intake manifold during the intake stroke. The proportion of DME in the total input energy was adjusted from 10% to 100%. DME DME injection timing was widely varied to investigate the effect of injection timing on the combustion phase. Injection pressure of DME was varied from 20 MPa to 60 MPa. Exhaust gas recirculation (EGR) was controlled from 0% to 60% to explore the effect of EGR on the combustion and emission characteristics. As DME proportion was decreased with the increased portion of gasoline, the combustion efficiency was decreased but thermal efficiency was increased.
Technical Paper

Effects of Single and Double Post Injections on Diesel PCCI Combustion

2013-03-25
2013-01-0010
In this study, single and double post injections were applied to diesel premixed charge compression ignition (PCCI) combustion to overcome the drawbacks those are high level of hydrocarbons (HC) and carbon monoxide (CO) emissions in a single-cylinder direct-injection diesel engine. The operating conditions including engine speed and total injection quantity were 1200 rpm and 12 mg/cycle, which are the representative of low engine speed and low load. The main injection timing of diesel PCCI combustion was set to 28 crank angle degree before top dead center (CAD BTDC). This main injection timing showed 32% lower level of nitric oxides (NOx) level and 8 CAD longer ignition delay than those of conventional diesel combustion. However, the levels of HC and CO were 2.7 and 3 times higher than those of conventional diesel combustion due to over-lean mixture and wall wetting of fuel.
Journal Article

Design and Modeling of a Novel Internal Combustion Engine with Direct Hydraulic Power Take-off

2013-04-08
2013-01-1733
This paper introduces a Hydraulic Linear Engine (HLE) concept and describes a model to simulate instantaneous engine behavior. The United States Environmental Protection Agency has developed an HLE prototype as an evolution of their previous six-cylinder, four-stroke, free-piston engine (FPE) hardware. The HLE design extracts work hydraulically, in a fashion identical to the initial FPE, and is intended for use in a series hydraulic hybrid vehicle. Unlike the FPE, however, the HLE utilizes a crank for improved timing control and increased robustness. Preliminary experimental results show significant speed fluctuations and cylinder imbalance that require careful controls design. This paper also introduces a model of the HLE that exhibits similar behavior, making it an indispensible tool for controls design. Further, the model's behavior is evaluated over a range of operating conditions currently unobtainable by the experimental setup.
Journal Article

Review of Soot Deposition and Removal Mechanisms in EGR Coolers

2010-04-12
2010-01-1211
Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOX emissions. Engine coolant is used to cool EGR coolers. The presence of a cold surface in the cooler causes fouling due to particulate soot deposition, condensation of hydrocarbon, water and acid. Fouling experience results in cooler effectiveness loss and pressure drop. In this study, possible soot deposition mechanisms are discussed and their orders of magnitude are compared. Also, probable removal mechanisms of soot particles are studied by calculating the forces acting on a single particle attached to the wall or deposited layer. Our analysis shows that thermophoresis in the dominant mechanism for soot deposition in EGR coolers and high surface temperature and high kinetic energy of soot particles at the gas-deposit interface can be the critical factor in particles removal.
Technical Paper

Improvement of Premixed Compression Ignition Combustion using Various Injector Configurations

2011-04-12
2011-01-1357
Premixed compression ignition (PCI) combustion was implemented using advanced injection strategy and exhaust gas recirculation in a direct-injection single-cylinder diesel engine. The injection timing swept experiment using a baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained three types of combustion regime: conventional diesel combustion for an injection timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for an injection timing of 40° CA BTDC and homogeneous charge compression ignition (HCCI) combustion for an injection timing of 80° CA BTDC. PCI combustion can be verified by burn duration analysis. The burn duration, which was defined as the period from 10% to 90% of the accumulated heat release, was very short in PCI combustion but not in the others. PCI combustion with an injection timing of 40° CA BTDC was achieved in a range of an exhaust gas recirculation (EGR) rate from 0% to around 40%.
Technical Paper

Mode Transition between Low Temperature Combustion and Conventional Combustion with EGR and Injection Modulation in a Diesel Engine

2011-04-12
2011-01-1389
Mode transition between low temperature combustion and conventional combustion was investigated in a direct injection diesel engine. Low temperature diesel combustion was realized by means of high exhaust gas recirculation rate (69~73%) and early injection timing (-28~ -16 crank angle degree after top dead center) compared with those (20% exhaust gas recirculation rate and -8 crank angle degree after top dead center) of conventional combustion. Tests were carried out at different engine speeds and injection pressures. Exhaust gas recirculation rate was changed transiently by controlling each throttle angle for fresh air and exhaust gas recirculation to implement mode transition. Various durations for throttle transition were applied to investigate the effect of speed change of exhaust gas recirculation rate on the characteristics of mode transition.
Technical Paper

The Influence of Fuel Injection Pressure and Intake Pressure on Conventional and Low Temperature Diesel Combustion

2012-09-10
2012-01-1721
The influence of fuel injection pressure and intake pressure on conventional and low temperature diesel combustion was investigated in a light duty diesel engine. The in-cylinder pressure and exhaust emissions were measured and analyzed in each operating condition. The two combustion regimes were classified in terms of intake oxygen concentrations, which were adjusted by varying the amount of exhaust gas recirculation. The fuel injection quantity and injection timing were fixed in order to minimize the influencing factors. Fuel injection pressures of 40 MPa and 120 MPa were used to verify the effect of the fuel injection pressure in both combustion regimes. The injection pressure significantly affected the combustion phase in the low temperature diesel combustion regime due to the longer premixing time relative to the conventional diesel combustion regime.
Technical Paper

Effect of the Multiple Injection on Stratified Combustion Characteristics in a Spray-Guided DISI Engine

2011-09-11
2011-24-0059
In this study, the single-cylinder engine experiment was carried out to investigate the effect of multiple injections on stratified combustion characteristics in a spray-guided direct injection spark ignition engine. The engine was operated at 1200 rpm. The total injection quantity applied was 11 mg/stroke to represent a low-load condition. Single injection and multiple injection were tested. Split ratio of each multiple strategies were 1:1 for double injection and 1:1:1 for the triple injection respectively. Dwell time between each injection was set to 200 μs. In the result of engine experiment with the single injection, indicated mean effective pressure was increased as injection timing was retarded to top dead center due to the increased effective work. However, the retardation of the injection timing was limited by the misfire occurrence resulted from the locally rich mixture generation under the high ambient pressure.
Technical Paper

Influence of EGR and Pilot Injection on PCCI Combustion in a Single-Cylinder Diesel Engine

2011-08-30
2011-01-1823
The effect of pilot injection and exhaust gas recirculation (EGR) on premixed charge compression ignition (PCCI) combustion was investigated in a single-cylinder direct-injection diesel engine with low engine speed and low load. The injection timing of PCCI combustion was fixed at 25 ~ 30 crank angle degree before top dead center (°CA BTDC) based on the ignition delay and power output. The level of oxides of nitrogen (NOx) emissions of PCCI combustion was 68% lower than that of conventional diesel combustion owing to the reduction of near-stoichiometric region which is well known as the main source of NOx formation. However, the indicated mean effective pressure (IMEP), hydrocarbon (HC), particulate matter (PM) and carbon monoxide (CO) emissions deteriorated compared with conventional diesel combustion because of early injection, advanced combustion phase and lowered combustion temperature. EGR has been applied to PCCI combustion.
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