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Technical Paper

EGR Interfaces: Modeling to Experimental Data Comparison

1998-10-19
982695
Motor vehicles emissions regulations become more and more stringent, concerning the air quality improvement. In that way, EGR technology ( like Exhaust Gas Recirculation ), with increasing recirculation flowrates, is more and more frequently applied [3]. If the manifold is made in polymer composites, problems appear at the EGR interface, because of material T° limits ( between 150° and 180 °C stabilized ). The study presents different goals: 1. To identify the major parameters leading to high manifold heat constraints; 2. To model the phenomena, to be able to extrapolate experimental results; 3. To get a practical tool, under abacus and model, helping designers to know the limits of the design, for one application, and so that, to be sure that the manifolds will not be overstressed in service. To get this, both experimental and numerical ways are taking into account. Let us remind that EGR is applied to limit NOx levels, and also fuel consumption by pumping losses limitation [3].
Technical Paper

Emission Formation Mechanisms in a Two-Stroke Direct-Injection Engine

1998-10-19
982697
Engine tests were conducted to study the effect of fuel-air mixture preparation on the combustion and emission performance of a two-stroke direct-injection engine. The in-cylinder mixture distribution was altered by changing the injection system, injection timing, and by substituting the air in an air-assisted injector with nitrogen. Two injection systems which produce significantly different mixtures were investigated; an air-assisted injector with a highly atomized spray, and a single-fluid high pressure-swirl injector with a dense penetrating spray. The engine was operated at overall A/F ratios of 30:1, where stratification was necessary to ensure stable combustion; and at 20:1 and 15:1 where it was possible to operate in a nearly homogeneous mode. Moderate engine speeds and loads were investigated. The effects of the burning-zone A/F ratio were isolated by using nitrogen as the working fluid in the air-assist injector.
Technical Paper

Schlieren Observations of In-Cylinder Phenomena Concerning a Direct-Injection Gasoline Engine

1998-10-19
982696
The schlieren visualization of in-cylinder processes from the side of an engine cylinder is useful to understand the phenomena which change along the cylinder axis. A transparent collimating cylinder, TCC, permits schlieren observation inside the cylinder through its transparent wall. In this study, a single cylinder visualization engine with the TCC was applied to a direct-injection gasoline engine. A fuel spray, mixture formation and combustion were observed with a simultaneous measurement of in-cylinder pressure. The shape of the fuel spray and subsequent mixture formation process are drastically changed with the injection timing. The images of luminous flame were also taken with the schlieren images during the combustion period. Stable combustion, misfire and abnormal combustion are discussed with the comparison between the observed results and in-cylinder pressure analysis.
Technical Paper

Effects of Injection Timing on Liquid-Phase Fuel Distributions in a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

1998-10-19
982699
An experimental study was carried out to investigate the effects of fuel injection timing on the spatial and temporal development of injected fuel sprays within a firing direct-injection spark-ignition (DISI) engine. It was found that the structure of the injected fuel sprays varied significantly with the timing of the injection event. During the induction stroke and the early part of the compression stroke, the development of the injected fuel sprays was shown to be controlled by the state of the intake and intake-generated gas flows at the start of injection (SOI).The relative influence of these two flow regimes on the injected fuel sprays during this period was also observed to change with injection timing, directly affecting tip penetration, spray/wall impingement and air-fuel mixing. Later in the compression stroke, the results show the development of the injected fuel sprays to be dominated by the increased cylinder pressure at SOI.
Technical Paper

Influence of Fuel Volatility on Emissions and Combustion in a Direct Injection Spark Ignition Engine

1998-10-19
982701
The purpose of this work was to investigate the influence of fuel parameters on emissions, combustion and cycle to cycle IMEP variations in a single cylinder version of a commercial direct injection stratified charge (DISC) spark ignition engine. The emission measurements employed both conventional emission measurement equipment as well as on-line gas chromatography/mass spectrometry (GC/MS). Four different fuels were compared in the study. The fuel parameters that were studied were distillation range and MTBE (Methyl Tert Buthyl Ether) content. A European certification gasoline fuel was used as a reference. The three other fuels contained 10% MTBE. The measurements were performed at a low engine speed and at a low, constant load. The engine was operated in stratified mode. The start of injection was altered 15 crankangle degrees before and after series calibration with fixed ignition timing in order to vary mixture preparation time.
Technical Paper

An attempt at Lean Burn of a4 Stroke Gasoline Engine by the Aid of Low Pressure Air Assisted In-Cylinder Injection

1998-10-19
982698
Lean burn engines now being developed employ in-cylinder injection which requires high pressures and so necessitates expensive injection equipment. The experiments reported here used air assisted in-cylinder injection, and injected a mixture of air and fuel during the intake stroke, so allowing atomization at lower injection pressures than those necessary in compressing fuel with solid injection. The experiments confirmed that operation in this manner resulted in similar output and fuel consumption as with a carburetor. Next, a divided combustion chamber was installed and connected to the main combustion chamber and air assisted in-cylinder injection from a reed type injection nozzle was attempted. With this arrangement, stable idling operation was possible to air-fuel ratios (A/F) of 70. Lean burn at A/F = 22 to 35 was also achieved at maximum rated outputs (3.7 kW at 4200 min-l) of 6 - 18 %.
Technical Paper

Effects of Injection Timing on the Exhaust Emissions of a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

1998-10-19
982700
A study to investigate the influence of fuel injection timing on exhaust emissions from a single-cylinder direct-injection spark-ignition (DISI) research engine was performed. Experimental results were obtained for carbon monoxide (CO), unburned hydrocarbon (HC), and oxides of nitrogen (NOx). Images showing the variation of liquid-phase fuel distribution with changing injection timing were obtained in a firing optically-accessed engine of similar design. A correlation between measured emissions and observed liquid-phase fuel distribution was performed. This correlation was supported by development of phenomenological models that permit explanation of the variation of CO, HC, and NOx emissions with changes in air-fuel mixture preparation.
Technical Paper

Visualization of Direct-Injection Gasoline Spray and Wall-impingement Inside a Motoring Engine

1998-10-19
982702
Two-dimensional pulse-laser Mie scattering visualization of the direct-injection gasoline fuel sprays and wall impingement processes was carried out inside a single-cylinder optically accessible engine under motoring condition. The injectors have been first characterized inside a pressurized chamber using identical technique, as well as high-speed microscopic visualization and phase Doppler measurement techniques. The effects of injector cone angle, location, and injection timings on the wall impingement processes were investigated. It was found that the fuel vaporization is not complete at the constant engine speed tested. Fuel spray droplets were observed to disperse wider in the motored engine when compared with an isothermal quiescent ambient conditions. The extent of wall-impingement varies significantly with the injector mounting position and spray cone angle; however, its effect can be reduced to some extent by optimizing the injection timing.
Technical Paper

Stability Improvement of Direct Fuel Injection Engine under Lean Combustion Operation

1998-10-19
982703
Meeting future exhaust emission and fuel consumption standards for passenger cars will require refinements in how the combustion process is carried out in spark ignition engines. A direct injection system reduces fuel consumption under road load cruising conditions, and stratified charge of the air-fuel mixture is particularly effective for lean combustion. This paper describes an approach to improve combustion stability for direct fuel injection gasoline engines. Effects of spray characteristics (spray pattern and diameter) and air flow motion on the combustion stability were investigated. Spray patterns were observed by the laser sheet scattering method and 3-dimensional laser doppler velocimetry. Mixture behavior in the combustion chamber was observed by the laser-induced fluorescence method using an excimer laser and single cylinder optical engine. It was found that the spray pattern for a pressurized condition affects the combustion stability and smoke generation.
Technical Paper

Stratified-Charge Engine Fuel Economy and Emission Characteristics

1998-10-19
982704
Data from two engines with distinct stratified-charge combustion systems are presented. One uses an air-forced injection system with a bowl-in-piston combustion chamber. The other is a liquid-only, high-pressure injection system which uses fluid dynamics coupled with a shaped piston to achieve stratification. The fuel economy and emission characteristics were very similar despite significant hardware differences. The contributions of indicated thermal efficiency, mechanical friction, and pumping work to fuel economy are investigated to elucidate where the efficiency gains exist and in which categories further improvements are possible. Emissions patterns and combustion phasing characteristics of stratified-charge combustion are also discussed.
Technical Paper

Catalyst Regeneration via Chemical Treatment and Emission Tests at Idle Speed

1998-10-19
982707
The present paper examines the possibility of chemical treatment of old catalysts (a catalyst that has exceeded exhaust limits) for the purpose of improving catalytic efficiency. The proposed method inserts the catalyst in a bath of a strong organic solvent that dissolves oil, soot and fuel residues cleaning the active surface of the catalyst. The preliminary experimental results based on CO, HC and catalyst inlet-outlet temperature difference measurements indicate that after this treatment the catalytic efficiency improves considerably (>30%). Therefore, there are strong indications that if car catalysts underwent a similar treatment at regular service intervals, for example, engine emissions could be considerably reduced and catalyst operational life extended. However more tests under variable engine speed (FTP-test) and load are clearly required in the future, before a definite conclusion can be made.
Technical Paper

Thermal Deterioration Mechanism of Pt/Rh Three-way Catalysts

1998-10-19
982706
To clarify the thermal deterioration mechanism of three-way catalysts quantitatively, we investigated the relationship between the catalytic performance and the catalyst characteristics for thermally aged Pt/Rh catalysts. 1. Experimentally, the HC oxidation reaction, which occurs on the surface of Pt/Rh particles on catalysts, is approximated by a first-order reaction of HC concentration with a constant activation energy. 2. The relationship between the Pt mean diameter D and the HC 50% conversion temperature T50 is described by the following equation; where E and kB are the activation energy of the reaction and the Boltzman constant, respectively. 3. The sintering rate of Pt particles on the three-way catalysts was found to depend on the aging temperature(T) of catalyst and the concentration of oxygen in the gas phase([O2]).
Technical Paper

The Effect of Different Traffic Conditions on Catalyst Performance and Exhaust Emissions of a 2-Liter Gasoline Car

1998-10-19
982708
In this paper the behavior of the three-way catalyst equipping a 2-liter car is fully analyzed considering exhaust gas and ceramic temperatures trends ( and of related engine parameters) in on-road operations of the car under different traffic conditions. These are classified by means of driving cycles clusters determined by multivariate statistical analysis of car speed and gear usage real profiles, detected on-road by the same car in designed experimental plans. Instantaneous fuel consumption and signals of a linear oxygen sensor, placed up-stream catalyst, have been analyzed to better characterize engine and catalyst performance. Emissions are measured in laboratory performing the most statistically representative driving cycles with car on the dynamometer chassis. The effect of traffic conditions on catalyst behavior and exhaust emissions is analyzed through the study of series of consecutive driving cycles.
Technical Paper

Emission Control Systems for Two Stroke Engines - A Challenge for Catalysis=

1998-10-19
982710
The exhaust emissions of two stroke vehicles like motorbikes and scooters contribute to the pollution in urban areas of developing countries in South East Asia and India to a major extent. But also in Japan and selected European countries exhaust gas limitations become effective from 10/1998 and 06/1999 for these vehicles. To control this emissions catalytic aftertreatment by Hot Tubes® and/or monolith type catalysts are applied. Due to the constant rich operation of the two-stroke engines, common design criteria for three-way catalysts fail. Extremely high exhaust gas hydrocarbon concentrations lead to high exotherms during oxidation which increases the exhaust gas temperature to a range between 800 and 900 °C. Furthermore the lack of oxygen limits the CO and HC oxidation under certain engine operation conditions. Therefore, water-gas shift and steam reforming reactions play an important part in catalytic aftertreatment of two-stroke exhausts.
Technical Paper

A Survey of Gasoline Fuel Deposit Control Additives in the Retail Aftermarket:Performance Claims vs. Chemistry

1998-10-19
982712
We purchased an assortment of retail aftermarket gasoline additives from many manufacturers with the intention of evaluating the contents to compare the active ingredients available in the package with the product performance and benefit claims as advertised on the label. We did an initial screening to determine a gross actives level through a low temperature non-volatile matter determination. We then sorted the products into groups according to their type of claim. Further infrared spectrographic analysis determined chemical content and confirmed the initial quantitative work. This information let us determine whether the manufacturer's choice of active ingredients was appropriate to provide the particular benefits claimed and whether there was enough to do the job.
Technical Paper

Field Test Study of Two-Stroke Catalytic Converter in Thailand

1998-10-19
982711
Technical feasibility study of the use of two-way catalytic converters in two-stroke motorcycles was conducted by means of a 20,000 km field-test. Three 150cc two-stroke motorcycles were retrofitted with metallic monolith catalyst. After the field test, the catalytic converters were inspected and found to be structurally intact and devoid of oil. The catalysts were not chemically poisoned. At the end of 20,000 km accumulation, the catalysts were still effective towards HC reduction. However, their light-off temperatures were shifted. White smoke was significantly reduced. However, a CO rise was observed throughout - indicating partial oxidation of HC due to insufficient availability of oxygen.
Technical Paper

Poisoning of Lambda Sensor: An Experimental Method to Measure the Lambda Sensor Switch Velocity and Its Effect on Air-Fuel Ratio Excursion

1998-10-19
982647
The development of the On-Board Diagnostic Systems (OBD) requires the determination of the critical level of the poisoning of the exhaust aftertreatment components. In order to have an accurate analysis, one way is to separate the effect of the poisoning of the two components: oxygen sensor and three way catalyst [ 1 ]. Our experimentation has been concentrated on poisoning of lambda sensor. An apparatus fed with model gases was realized to evaluate the poisoning of oxygen sensors coming from a fleet test of 6 taxis after a mileage of 100000 km. Our apparatus has been able to differentiate the poisoning level of the sensors by measuring their “switchability”. To confirm these measurements the lambda sensor switchability has been verified with a bench test using the Mercedes- Benz M111E engine. Exposing the aged lambda sensor to the engine exhaust gas, its response was coherent with its behavior on the apparatus fed with model gases.
Technical Paper

Effect of Fuel Compositions on PAH in Particulate Matter from DI Diesel Engine

1998-10-19
982648
The effects of fuel properties on poly aromatic hydrocarbons (PAHs) in particulate matter from the latest DI diesel engine were investigated under the Japanese 13 mode test cycle. It was found that the deeply desulfurized fuel had large effect on reducing PAH emissions. Furthermore, the reduction of PAH emissions was observed in the case of kerosene blend on the high sulfur fuel. However, the reduction of PAH emissions due to kerosene blend was not so large in the deeply desulfurized fuel. From the test using special fuel of which target property only changed under keeping the rest propeties constant, it was suggested that poly aromatics in the fuel affected PAH emissions and the influence of tri-aromatics in the fuel was promoted by the coexistence of mono-aromatics or naphthene. PAH formation scheme from each fuel component was proposed by chemical thermodynamic data.
Technical Paper

Interactions Between Exhaust Gas Composition and Oxygen Sensor Performance

1998-10-19
982646
While oxygen sensors provide the means by which changes in exhaust gas AFR (air-to-fuel ratio) are monitored and controlled in three-way catalyst systems, the chemistry of the exhaust gas in contact with this solid state electrochemical sensor can exert a substantial influence on its AFR control performance. Such interactions have been examined in a fundamental study on commercial oxygen sensors (unheated and heated), firstly using simple gas mixtures, and then simulated exhaust gas mixtures of progressively increasing complexity. The work confirms that diffusion effects at the sensor surface are centrally important in determining sensor response, but indicate that the effects of H2 (the smallest species present) do not necessarily dominate the observed behaviour. The results allow the development of a relationship that can be used to estimate the extent of the expected overall lean or rich shift for the sensor as a function of the exhaust gas composition.
Technical Paper

Contribution of Cold and Hot Start Transients in Engine-out HC Emissions

1998-10-19
982645
Engine-out HC emissions were investigated during cold and hot starts. The tests were conducted at room temperature, on a new Chrysler 2.4-L, 4-cylinder, 16-valve, DOHC, multipoint-port-fuel-injection gasoline engine. Real time engine-out HC emissions were measured using Cambustion Fast Response Flame Ionization Detector (FRFID). Sources of unburned hydrocarbon emissions were discussed in details. Unburned hydrocarbons emitted during the cold-start were much higher than the hot-start. Cylinder-to-cylinder variation was investigated. A fuel inventory program was used to characterize total injected fuel, burned fuel, unburned HC, and fuel unaccounted for (mainly accumulated fuel in the engine system and CO). A fuel interrupt test was run to examine the possibility of burning the leftover fuel after the fuel shut-off. The contribution of the cold and hot start modes in engine-out HC emissions was determined.
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