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Technical Paper

Effect of In-Cylinder Liquid Fuel Films on Engine-Out Unburned Hydrocarbon Emissions for an SI Engine

2012-09-10
2012-01-1712
An experimental study was performed in a firing SI engine at conditions representative of the warmup phase of operation in which liquid gasoline films were established at various locations in the combustion chamber and the resulting impact on hydrocarbon emissions was assessed. Unique about this study was that it combined, in a firing engine environment, direct visual observation of the liquid fuel films, measurements of the temperatures these films were subjected to, and the determination from gas analyzers of burned and unburned fuel quantities exiting the combustion chamber - all with cycle-level resolution or better. A means of deducing the exhaust hydrocarbon emissions that were due to the liquid fuel films in the combustion chamber was developed. An increase in exhaust hydrocarbon emissions was always observed with liquid fuel films present in the combustion chamber.
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.
Technical Paper

Evaluation of a One-Zone Burn-Rate Analysis Procedure Using Production SI Engine Pressure Data

1993-10-01
932749
A single-zone burn-rate analysis based on measured cylinder pressure data proposed by Gatowski et al. in 1984 was evaluated over the full load and speed range of a spark-ignition engine. The analysis, which determines the fuel mass burning rate based on the First Law of Thermodynamics, includes sub-models for the effects of residual fraction, heat transfer, and crevices. Each of these sub-models was assessed and calibrated. Cylinder pressure data over the full engine operating range obtained from two different engines were used to examine the robustness of the analysis. The sensitivity of predictions to the parameters wall temperature, heat transfer model coefficients and exponent, swirl ratio, motoring polytropic constant, in-cylinder mass, and to uncertainty in pressure data was evaluated.
Technical Paper

A Model for Converting SI Engine Flame Arrival Signals into Flame Contours

1995-02-01
950109
A model which converts flame arrival times at a head gasket ionization probe, used in a spark-ignition engine, into flame contours has been developed. The head gasket was manufactured at MIT using printed circuit board techniques. It has eight electrodes symmetrically spaced around the circumference (top of cylinder liner) and it replaces the conventional head gasket. The model is based on engine flame propagation rate data taken from the literature. Data from optical studies of S.I. engine combustion or studies utilizing optical fiber or ionization probe diagnostics were analyzed in terms of the apparent flame speed and the entrainment speed (flame speed relative to the fluid ahead of the flame). This gives a scaling relationship between the flame speed and the mass fraction burned which is generic and independent of the chamber shape.
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

The Influence of Operating Variables and Prechamber Size on Combustion in a Prechamber Stratified-Charge Engine

1978-02-01
780966
This paper describes the results of experimental and computer simulation studies of the combustion process in the prechamber three-valve stratified-charge engine. Prechamber and main-chamber pressure data and matched computer simulation calculations are used to determine the effects of variations in overall air/fuel ratio, engine speed and load, and prechamber volume and orifice diameter on the parameters which define the combustion process (spark advance for optimum torque, ignition delay, combustion duration), on cylinder pressure diagrams (mean main-chamber pressure, mean pressure difference across the orifice, and cycle-by-cycle pressure fluctuations) and on exhaust emissions. General correlations are derived from the data for the shape of the combustion rate profile and the extent of the combustion duration.
Technical Paper

The Effect of Chamber Geometry on Spark-Ignition Engine Combustion

1983-02-01
830334
The way In which combustion chamber geometry affects combustion in SI engines was studied using a quasi-diraensional cycle simulation. Calculations were performed to investigate the following questions: (i) the sensitivity of geometric effects on combustion to engine operating conditions; (ii) the differences in burn duration between ten chamber geometries and spark plug locations; and (iii) the relative merits of improved chamber design and amplified turbulence as means to reduce burn duration. The results from these studies are presented and discussed.
Technical Paper

Analysis of Hydrocarbon Emissions Mechanisms in a Direct Injection Spark-Ignition Engine

1983-02-01
830587
The direct injection spark-ignition engine is the only internal combustion engine with the potential to equal the efficiency of the diesel and to tolerate a wide range of fuel types and fuel qualities without deterioration of performance. However, this engine has low combustion efficiency and excessive hydrocarbon emissions when operating at light load. In this paper, potential sources of hydrocarbon emissions during light load operation are postulated and analyzed. The placement of fuel away from the primary combustion process in conjunction with a lack of secondary burnup are isolated as important hydrocarbon emissions mechanisms. Analyses show that increasing cylinder gas temperatures can improve secondary burnup of fuel which would reduce hydrocarbon emissions. Practical means to achieve this include higher compression ratio and use of ceramic parts in the combustion chamber.
Technical Paper

Heat Release Analysis of Engine Pressure Data

1984-10-01
841359
In analyzing the processes inside the cylinder of an internal combustion engine, the principal diagnostic at the experimenter's disposal is a measured time history of the cylinder pressure. This paper develops, tests, and applies a heat release analysis procedure that maintains simplicity while including the effects of heat transfer, crevice flows and fuel injection. The heat release model uses a one zone description of the cylinder contents with thermodynamic properties represented by a linear approximation for γ(T). Applications of the analysis to a single-cylinder spark-ignition engine, a special square cross-section visualization spark-ignition engine, and a direct-injection stratified charge engine are presented.
Technical Paper

Development and Use of a Computer Simulation of the Turbocompounded Diesel System for Engine Performance and Component Heat Transfer Studies

1986-03-01
860329
A computer simulation of the turbocharged turbocompounded direct-injection diesel engine system has been developed in order to study the performance characteristics of the total system as major design parameters and materials are varied. Quasi-steady flow models of the compressor, turbines, manifolds, intercooler, and ducting are coupled with a multi-cylinder reciprocator diesel model where each cylinder undergoes the same thermodynamic cycle. Appropriate thermal loading models relate the heat flow through critical system components to material properties and design details. This paper describes the basic system models and their calibration and validation against available experimental engine test data. The use of the model is illustrated by predicting the performance gains and the component design trade-offs associated with a partially insulated engine achieving a 40 percent reduction in heat loss over a baseline cooled engine.
Technical Paper

Mixture Preparation Mechanisms in a Port Fuel Injected Engine

2005-05-11
2005-01-2080
An experimental study was carried out that qualitatively examined the mixture preparation process in port fuel injected engines. The primary variables in this study were intake valve lift, intake valve timing, injector spray quality, and injection timing. A special visualization engine was used to obtain high-speed videos of the fuel-air mixture flowing through the intake valve, as well as the wetting of the intake valve and head in the combustion chamber. Additionally, videos were taken from within the intake port using a borescope to examine liquid fuel distribution in the port. Finally, a simulation study was carried out in order to understand how the various combinations of intake valve lifts and timings affect the flow velocity through the intake valve gap to aid in the interpretation of the videos.
Technical Paper

Effects of Combustion Phasing, Relative Air-fuel Ratio, Compression Ratio, and Load on SI Engine Efficiency

2006-04-03
2006-01-0229
In an effort to both increase engine efficiency and generate new, consistent, and reliable data useful for the development of engine concepts, a modern single-cylinder 4-valve spark-ignition research engine was used to determine the response of indicated engine efficiency to combustion phasing, relative air-fuel ratio, compression ratio, and load. Combustion modeling was then used to help explain the observed trends, and the limitations on achieving higher efficiency. This paper analyzes the logic behind such gains in efficiency and presents correlations of the experimental data. The results are helpful for examining the potential for more efficient engine designs, where high compression ratios can be used under lean or dilute regimes, at a variety of loads.
Technical Paper

Predicting the Behavior of a Hydrogen-Enhanced Lean-Burn SI Engine Concept

2006-04-03
2006-01-1106
This paper explores the modeling of a lean boosted engine concept. Modeling provides a useful tool for investigating different parameters and comparing resultant emissions and fuel economy performance. An existing architectural concept has been tailored to a boosted hydrogen-enhanced lean-burn SI engine. The simulation consists of a set of Matlab models, part physical and part empirical, which has been developed to simulate a working engine. The model was calibrated with production engine data and experimental data taken at MIT. Combustion and emissions data come from a single cylinder research engine and include changes in air/fuel ratio, load and speed, and different fractions of the gasoline fuel reformed to H2 and CO. The outputs of the model are brake specific NOx emissions and brake specific fuel consumption maps along with cumulative NOx emissions and fuel economy for urban and highway drive cycles.
Technical Paper

Engine Knock Characteristics at the Audible Level

1991-02-01
910567
The effects of combustion chamber and intake valve deposit build-up on the knocking characteristics of a spark ignition engine were studied. A Chrysler 2.2 liter engine was run continuously for 180 hours to build up intake valve and combustion chamber deposits. In the tests reported here, the gasoline used contained a deposit controlling fuel additive. The engines's octane requirement increased by 10 research octane numbers during this extended engine operating period. At approximately 24 hour intervals during these tests, the engine was audibly knock rated to determine its octane requirement. Cylinder pressure data was collected during knocking conditions to investigate the knocking characteristics of each cylinder, and deposit build-up effects on those statistics. Cylinder-to-cylinder variations in knock statistics were studied. Analysis of the data indicated that some 20 to 40 percent of cycles knock before the knock is audibly detected.
Technical Paper

The Effect of Piston Temperature on Hydrocarbon Emissions from a Spark-Ignited Direct-Injection Engine

1991-02-01
910558
Light-load unburned hydrocarbon emissions were studied experimentally in a spark-ignited direct-injection engine burning gasoline where the piston temperature was varied. The test engine was a single-cylinder Direct Injection Stratified-Charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System. At a single low load operating condition, the piston temperature was varied by 50 K by controlling the cooling water and oil temperature. The effect of this change on unburned hydrocarbon emissions and heat release profiles was studied. It was found that by carefully controlling the intake air temperature and pressure to maintain constant in-cylinder conditions at the time of injection, the change in piston temperature did not have a significant effect on the unburned hydrocarbon emissions from the engine.
Technical Paper

Modeling the Spark Ignition Engine Warm-Up Process to Predict Component Temperatures and Hydrocarbon Emissions

1991-02-01
910302
In order to understand better the operation of spark-ignition engines during the warm-up period, a computer model had been developed which simulates the thermal processes of the engine. This model is based on lumped thermal capacitance methods for the major engine components, as well as the exhaust system. Coolant and oil flows, and their respective heat transfer rates are modeled, as well as friction heat generation relations. Piston-liner heat transfer is calculated based on a thermal resistance method, which includes the effects of piston and ring material and design, oil film thickness, and piston-liner crevice. Piston/liner crevice changes are calculated based on thermal expansion rates and are used in conjunction with a crevice-region unburned hydrocarbon model to predict the contribution to emissions from this source.
Technical Paper

Phenomena that Determine Knock Onset in Spark-Ignition Engines

2007-01-23
2007-01-0007
Experiments were carried out to collect in-cylinder pressure data and microphone signals from a single-cylinder test engine using spark timingsbefore, at, and after knock onset for toluene reference fuels. The objective was to gain insight into the phenomena that determine knock onset, detected by an external microphone. In particular, the study examines how the end-gas autoignition process changes as the engine's spark timing is advanced through the borderline knock limit into the engine's knocking regime. Fast Fourier transforms (FFT) and bandpass filtering techniques were used to process the recorded cylinder pressure data to determine knock intensities for each cycle. Two characteristic pressure oscillation frequencies were detected: a peak just above 6 kHz and a range of peaks in the 15-22 kHz range. The microphone data shows that the audible knock signal has the same 6 kHz peak.
Technical Paper

An Overview of Hydrocarbon Emissions Mechanisms in Spark-Ignition Engines

1993-10-01
932708
This paper provides an overview of spark-ignition engine unburned hydrocarbon emissions mechanisms, and then uses this framework to relate measured engine-out hydrocarbon emission levels to the processes within the engine from which they result. Typically, spark-ignition engine-out HC levels are 1.5 to 2 percent of the gasoline fuel flow into the engine; about half this amount is unburned fuel and half is partially reacted fuel components. The different mechanisms by which hydrocarbons in the gasoline escape burning during the normal engine combustion process are described and approximately quantified. The in-cylinder oxidation of these HC during the expansion and exhaust processes, the fraction which exit the cylinder, and the fraction oxidized in the exhaust port and manifold are also estimated.
Technical Paper

Predicting the Effects of Air and Coolant Temperature, Deposits, Spark Timing and Speed on Knock in Spark Ignition Engines

1992-10-01
922324
The prediction of knock onset in spark-ignition engines requires a chemical model for the autoignition of the hydrocarbon fuel-air mixture, and a description of the unburned end-gas thermal state. Previous studies have shown that a reduced chemistry model developed by Keck et al. adequately predicts the initiation of autoignition. However, the combined effects of heat transfer and compression on the state of the end gas have not been thoroughly investigated. The importance of end-gas heat transfer was studied with the objective of improving the ability of our knock model to predict knock onset over a wide range of engine conditions. This was achieved through changing the thermal environment of the end gas by either varying the inlet air temperature or the coolant temperature. Results show that there is significant heating of the in-cylinder charge during intake and a substantial part of the compression process.
Technical Paper

Mixture Preparation in a SI Engine with Port Fuel Injection During Starting and Warm-Up

1992-10-01
922170
The in-cylinder hydrocarbon (HC) mole fraction was measured on a cycle-resolved basis during simulated starting and warm-up of a port-injected single-cylinder SI research engine on a dynamometer. The measurements were made with a fast-response flame ionization detector with a heated sample line. The primary parameters that influence how rapidly a combustible mixture builds up in the cylinder are the inlet pressure and the amount of fuel injected; engine speed and fuel injection schedule have smaller effects. When a significant amount of liquid fuel is present at the intake port in the starting process, the first substantial firing cycle is often preceded by a cycle with abnormally high in-cylinder HC and low compression pressure. An energy balance analysis suggests that a large amount of liquid vaporization occurs within the cylinder in this cycle.
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