Refine Your Search

Topic

Author

Search Results

Technical Paper

Modeling NO Formation in Spark Ignition Engines with a Layered Adiabatic Core and Combustion Inefficiency Routine

2001-03-05
2001-01-1011
A thermodynamic based cycle simulation which uses a thermal boundary layer, either, a fully mixed or layered adiabatic core, and a crevice combustion inefficiency routine has been used to explore the sensitivity of NO concentration predictions to critical physical modeling assumptions. An experimental database, which included measurements of residual gas fraction, was obtained from a 2.0 liter Nissan engine while firing on propane. A model calibration methodology was developed to ensure accurate predictions of in-cylinder pressure and burned gas temperature. Comparisons with experimental NO data then showed that accounting for temperature stratification during combustion with a layered adiabatic core and including a crevice/combustion inefficiency routine, improved the match of modeling predictions to data, in comparison to a fully mixed adiabatic core.
Technical Paper

Effects of Gas Flow and Mixture Properties on Engine-Out HC Emissions

1996-10-01
961952
The geometry and area of the notch in the swirl control valve installed in the intake port were varied to analyze the effects on HC emissions. A swirl control valve functions to promote the formation of a homogeneous mixture, enabling the amount of liquid fuel supplied to the cylinder to be reduced. For this reason, it is difficult to obtain an added effect through the combined use of a swirl control valve and an auxiliary-air type of injector for assisting fuel atomization. Tumble (vertical swirl) flow fields are effective in shortening the combustion period. This results in a higher exhaust gas temperature at an equivalent level of combustion stability. It was thought that swirl flow fields produce residual gas flow in the cylinder after the completion of the main combustion period. It is surmised that the residual gas flow functions to diffuse and promote after-burning of the unburned HC layer.
Technical Paper

Effects of Swirl/Tumble Motion on In-Cylinder Mixture Formation in a Lean-Burn Engine

1996-10-01
961994
Flow measurement by laser Doppler velocimetry and visualization of in-cylinder fuel vapor motion by laser induced fluorescence were performed for various types of intake systems that generated several different combinations of swirl and tumble ratios. The measured results indicate that certain swirl and tumble ratios are needed to achieve charge stratification in the cylinder. Performance tests were also carried out to determine the combustion characteristics of each intake system. Then, the features of combustion when the charge stratification was realized was analyzed.
Technical Paper

Liquid Fuel Transport Mechanisms into the Cylinder of a Firing Port-Injected SI Engine During Start Up

1997-02-24
970865
The occurrence of liquid fuel in the cylinder of automotive internal combustion engines is believed to be an important source of exhaust hydrocarbon (HC) emissions, especially during the warm-up process following an engine start up. In this study a Phase Doppler Particle Analyzer (PDPA) has been used in a transparent flow visualization combustion engine in order to investigate the phenomena which govern the transport of liquid fuel into the cylinder during a simulated engine start up process. Using indolene fuel, the engine was started up from room temperature and run for 90 sec on each start up simulation. The size and velocity of the liquid fuel droplets entering the cylinder were measured as a function of time and crank angle position during these start up processes. The square-piston transparent engine used gave full optical access to the cylinder head region, so that these droplet characteristics could be measured in the immediate vicinity of the intake valve.
Technical Paper

Development of a High-Pressure Fueling System for a Direct-Injection Gasoline Engine

1998-05-04
981458
A direct-injection gasoline engine that uses a stratified charge combustion process was developed by Nissan and released in the Japanese market toward the end of 1997. This new engine is based on Nissan's VQ engine, which enjoys a good reputation for its quick throttle response and low fuel consumption, and has been developed to accomplish the objectives of reducing fuel consumption by stratified charge combustion and securing high power output. The fuel injectors are connected by an arrangement of lightweight, small-diameter fuel lines that distribute fuel to each injector under high pressure. This system was adopted in order to reconcile the use of an aerodynamic straight intake port with the desired fuel injection position. The use of a casting net injector, which uniformly distributes the fuel spray above the piston, makes it possible to accomplish stratified charge combustion with a shallow-bowl piston.
Technical Paper

Numerical Optimization of the Fuel Mixing Process in a Direct-Injection Gasoline Engine

1998-05-04
981440
The spray formation and mixing processes in a direct-injection gasoline engine are examined by using a sophisticated air flow calculation model and an original spray model. The spray model for a spiral injector can evaluate the droplet size and spatial distribution under a wide range of parameters such as the initial cone angle, back pressure and injection pressure. This model also includes the droplet breakup process due to wall impingement. The arbitrary constants used in the spray model are derived theoretically without using any experimental data. Fuel vapor distributions just before ignition and combustion processes are analyzed for both homogeneous and stratified charge conditions.
Technical Paper

Mixture Formation and Combustion Performance in a New Direct-Injection SI V-6 Engine

1998-05-04
981435
One advantage of a direct-injection S.I. engine is lower fuel consumption due to the use of lean stratified charge combustion. Another advantage is greater power output resulting from evaporation of the fuel in the cylinder. A critical factor in making the most of these advantages is to achieve optimum mixture formation for both stratified and homogeneous charge combustion. To achieve the optimum mixture, the new direct-injection S.I. V-6 engine adopts a piston with a shallow bowl, a valve that changes in-cylinder air motion between swirl and tumble by opening and closing one side of separated air intake port, an air intake port that has optimized inward and port angle to induces swirl in the piston bowl, and a CASTING NET injector that injects the hollow cone spray in a deflected pattern toward the spark plug.
Technical Paper

Analysis of Fuel Behavior in the Spark-Ignition Engine Start-Up Process

1995-02-01
950678
An analysis method for characterizing fuel behavior during spark-ignition engine starting has been developed and applied to several sets of start-up data. The data sets were acquired from modern production vehicles during room temperature engine start-up. Two different engines, two control schemes, and two engine temperatures (cold and hot) were investigated. A cycle-by-cycle mass balance for the fuel was used to compare the amount of fuel injected with the amount burned or exhausted as unburned hydrocarbons. The difference was measured as “fuel unaccounted for”. The calculation for the amount of fuel burned used an energy release analysis of the cylinder pressure data. The results include an overview of starting behavior and a fuel accounting for each data set Overall, starting occurred quickly with combustion quality, manifold pressure, and engine speed beginning to stabilize by the seventh cycle, on average.
Technical Paper

Turbulence and Cycle-by-Cycle Variation of Mean Velocity Generated by Swirl and Tumble Flow and Their Effects on Combustion

1995-02-01
950813
Combinations of swirl flow and tumble flow generated by 13 types of swirl control valve were tested by using both impulse steady flow rig and LDV. Comparison between the steady flow characteristics and the result of LDV measurement under motoring condition shows that tumble flow generates turbulence in combustion chamber more effectively than swirl flow does, and that swirling motion reduces the cycle by cycle variation of mean velocity in combustion chamber which tends to be generated by tumbling motion. Performance tests are also carried out under the condition of homogeneous charge. Tumble flow promotes the combustion speed more strongly than expected from its turbulence intensity measured by LDV. It is also shown that lean limit air fuel ratio does not have a strong relation with cycle variation of mean velocity but with turbulence intensity.
Technical Paper

Effect of Engine Design/Control Parameters and Emission Control Systems on Specific Reactivity of S.I. Engine Exhaust Gases

1995-02-01
950807
In 1994, the California Air Resources Board implemented low-emission vehicle (LEV) standards with the aim of improving urban air quality. One feature of the LEV standards is the increasingly tighter regulation of non-methane organic gases (NMOG), taking into account ozone formation, in addition to the existing control of non-methane hydrocarbons (NMHC). Hydrocarbons and other organic gases emitted by S.I. engines have been identified as a cause of atmospheric ozone formation. Since the reactivity of each chemical species in exhaust emissions differs, the effect on ozone formation varies depending on the composition of the exhaust gas components. This study examined the effect of different engine types, fuel atomization conditions, turbulence and emission control systems on emission species and specific reactivity. This was done using gas chromatographs and a high-performance liquid chromatograph to analyze exhaust emission species that affect ozone formation.
Technical Paper

A Study of Cycle-to-Cycle Variations in SI Engines Using a Modified Quasi-Dimensional Model

1996-05-01
961187
This paper describes the use of a modified quasi-dimensional spark-ignition engine simulation code to predict the extent of cycle-to-cycle variations in combustion. The modifications primarily relate to the combustion model and include the following: 1. A flame kernel model was developed and implemented to avoid choosing the initial flame size and temperature arbitrarily. 2. Instead of the usual assumption of the flame being spherical, ellipsoidal flame shapes are permitted in the model when the gas velocity in the vicinity of the spark plug during kernel development is high. Changes in flame shape influence the flame front area and the interaction of the enflamed volume with the combustion chamber walls. 3. The flame center shifts due to convection by the gas flow in the cylinder. This influences the flame front area through the interaction between the enflamed volume and the combustion chamber walls. 4. Turbulence intensity is not uniform in cylinder, and varies cycle-to-cycle.
Technical Paper

Three-Dimensional Computation of the Effects of the Swirl Ratio in Direct-Injection Diesel Engines on NOx and Soot Emissions

1996-05-01
961125
Three-dimensional computation has been applied to analyze combustion and emission characteristics in direct-injection diesel engines. A computational code called TurboKIVA was used to investigate the effects of the swirl ratio, one of the fundamental factors related to combustion control, on combustion characteristics and NOx and soot emissions. The code was first modified to calculate soot formation and oxidation and the precise behavior of fuel drops on the combustion chamber wall. As a result of improving calculation accuracy, good agreement was obtained between the measured and predicted pressure, heat release rate and NOx and soot emissions. Using this modified version of TurboKIVA, the effects of the swirl ratio on NOx and soot emissions were investigated. The computational results showed that soot emissions were reduced with a higher swirl ratio. However, a further increase in the swirl ratio produced greater soot emissions.
Technical Paper

Development of a Valve Train Wear Test Procedure for Gasoline Engine Oil

1994-03-01
940794
An analysis was made of wear factors by investigating the effect of engine operating conditions on valve train wear. It was found that cam nose wear increased as larger amounts of combustion products, including nitrogen oxides and unburned gasoline, became intermixed with the engine oil. Based on these results, a valve train wear test procedure has been developed for evaluating cam nose and rocker arm wear under engine firing conditions. It has been confirmed that this test procedure correlates will with ASTM Sequence VE test and CCMC TU-3 test.
Technical Paper

Liquid Gasoline Behavior in the Engine Cylinder of a SI Engine

1994-10-01
941872
The liquid fuel entry into the cylinder and its subsequent behavior through the combustion cycle were observed by a high speed CCD camera in a transparent engine. The videos were taken with the engine firing under cold conditions in a simulated start-up process, at 1,000 RPM and intake manifold pressure of 0.5 bar. The variables examined were the injector geometry, injector type (normal and air-assisted), injection timing (open- and closed-valve injection), and injected air-to-fuel ratios. The visualization results show several important and unexpected features of the in-cylinder fuel behavior: 1) strip-atomization of the fuel film by the intake flow; 2) squeezing of fuel film between the intake valve and valve seat at valve closing to form large droplets; 3)deposition of liquid fuel as films distributed on the intake valve and head region. Some of the liquid fuel survives combustion into the next cycle.
Technical Paper

Simultaneous Attainment of Low Fuel Consumption High Output Power and Low Exhaust Emissions in Direct Injection SI Engines

1998-02-01
980149
This paper describes simultaneous attainment in improving fuel consumption, output power and reducing HC emissions with a direct injection S.I. engine newly developed in Nissan. Straight intake port is adopted to increase discharge coefficient under WOT operation and horizontal swirl flow is generated by a swirl control valve to provide stable stratified charge combustion under part load conditions. As a result, fuel consumption is reduced by more than 20% and power output is improved by approximately 10%. Moreover, unburned HC is reduced by equivalently 30% in engine cold start condition. An application of diagnostic and numerical simulation tools to investigate and optimize various factors are also introduced.
Technical Paper

Engine-Out and Tail-Pipe Emission Reduction Technologies of V-6 LEVs

1998-02-23
980674
Compared with in-line 4-cylinder engines, V-6 engines show a slower rise in exhaust gas temperature, requiring a longer time for catalysts to become active, and they also emit higher levels of engine-out emissions. In this study, The combination of a new type of catalyst, and optimized ignition timing and air-fuel ratio control achieved quicker catalyst light-off. Additionally, engine-out emissions were substantially reduced by using a swirl control valve to strengthen in-cylinder gas flow, adopting electronically controlled exhaust gas recirculation (EGR), and reducing the crevice volume by decreasing the top land height of the pistons. A vehicle incorporating these emission reduction technologies reduced the emission level through the first phase of the Federal Test Procedure (FTP) by 60-70% compared with the Tier 1 vehicle.
Technical Paper

The Effect of Operating Conditions at Idle in the S.I. Engine

1997-10-01
972990
A gasoline engine with an electronically controlled fuel injection system has substantially better fuel economy and lower emissions than a carburetted engine. In general, the stability of engine operation is improved with fuel injector, but the stability of engine operation at idle is not improved compared with a carburetted gasoline engine. In addition, the increase in time that an engine is at idle due to traffic congestion has an effect on the engine stability and vehicle reliability. Therefore, in this research, we will study the influence of fuel injection timing, spark timing, dwell angle, and air-fuel ratio on engine stability at idle.
Technical Paper

Engine-Out “Dry” Particular Matter Emissions from SI Engines

1997-10-01
972890
The Engine-Out Particulate Matter (EOPM) was collected from a spark ignition engine operating in steady state using a heated quartz fiber filter. The samples were weighted to obtain an EOPMindex and were analyzed using Scanning Electron Microscopy. The EOP Mindex was not sensitive to the engine rpm and load. When the mixture is very rich (air equivalence ratio λ less than ∼ 0.7), the EOPM comprise mostly of soot particles from fuel combustion. In the lean to slightly rich region (0.8 < λ < 1.2), however, the EOPM are dominated by particles derived from the lubrication oil.
Technical Paper

A Model for Flame Initiation and Early Development in SI Engine and its Application to Cycle-to-Cycle Variations

1994-10-01
942049
This paper uses a model which calculates the flame kernel formation and its early development in spark ignition engines to examine the causes of cycle-to-cycle combustion variations. The model takes into account the primary physical factors influencing flame development. The spark-generated flame kernel size and temperature required to initialize the computation are completely determined by the breakdown energy and the heat conduction from burned region to unburned region. In order to verify the model, the computation results are compared with high-speed Schlieren photography flame development data from an operating spark-ignition engine; they match remarkably well with each other at all test conditions. For the application of this model to the study of cycle-to-cycle variation of the early stage of combustion, additional input is required.
Technical Paper

Flame Shape Determination Using an Optical-Fiber Spark Plug and a Head-Gasket Ionization Probe

1994-10-01
941987
A method for determining the flame contour based on the flame arrival time at the fiber optic (FO) spark plug and at the head gasket ionization probe (IP) locations has been developed. The experimental data were generated in a single-cylinder Ricardo Hydra spark-ignition engine. The head gasket IP, constructed from a double-sided copper-clad circuit board, detects the flame arrival time at eight equally spaced locations at the top of the cylinder liner. Three other IP's were also installed in the cylinder head to provide additional intermediate data on flame location and arrival time. The FO spark plug consists of a standard spark plug with eight symmetrically spaced optical fibers located in the ground casing of the plug. The cylinder pressure was recorded simultaneously with the eleven IP signals and the eight optical signals using a high-speed PC-based data acquisition system.
X