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Technical Paper

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

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

A Rapid Compression Machine Study of the Influence of Charge Temperature on Diesel Combustion

Difficulties in the starting and operation of diesel engines at low temperatures are an important consideration in their design and operation, and in selection of the fuels for their use. Improvements in operation have been achieved primarily through external components of the engine and associated subsystems. A Rapid Compression Machine (RCM) has been modified to operate over a wide range of temperatures (−20°C to 100°C). It is used to isolate the combustion chamber in an environment in which all significant parameters are carefully defined and monitored. The influence of temperature and cetane number on the ignition and combustion processes are analyzed. Examination of the combustion characteristics show that temperature is by far the most influential factor affecting both ignition delay and heat release profiles. Cetane number (ASTM D-613) is not found to be a strong indicator of ignition delay for the conditions investigated.
Technical Paper

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

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

Aggregate Emissions from the Automobile Population

A methodology is presented with which aggregate emissions from the in-use automobile population can be calculated for any given calendar year. The data base needed for such a calculation is discussed, and areas in which further research is needed are pointed out. Results of a series of calculations are then presented showing the effect on aggregate emissions of various control strategies. The effects of an inspection/maintenance and retrofit program, different vehicle population growth rates, catalyst deterioration in use, and various schedules of new car emission standards for post-1975 vehicles are presented. It is shown that the rate at which old, higher-polluting vehicles are retired from the in-use vehicle population is the major factor in determining the rate at which aggregate emissions will decrease in the 1970s, with the precise level of post-1975 standards only becoming important in the 1980s.
Technical Paper

An Improved Friction Model for Spark-Ignition Engines

A spark-ignition engine friction model developed by Patton et al. in the late 1980s was evaluated against current engine friction data, and improved. The model, which was based on a combination of fundamental scaling laws and empirical results, includes predictions of rubbing losses from the crankshaft, reciprocating, and valvetrain components, auxiliary losses from engine accessories, and pumping losses from the intake and exhaust systems. These predictions were based on engine friction data collected between 1980 and 1988. Some of the terms are derived from lubrication theory. Other terms were derived empirically from measurements of individual friction components from engine teardown experiments. Recent engine developments (e.g., improved oils, surface finish on piston liners, valve train mechanisms) suggested that the model needed updating.
Technical Paper

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

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

Analysis of Oil Consumption Behavior during Ramp Transients in a Production Spark Ignition Engine

Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contributes directly to hydrocarbon and particulate emissions. In addition, chemical compounds present in oil additives poison catalytic converters and reduce their conversion efficiency. Oil consumption can increase significantly during critical non-steady operating conditions. This study analyzes the oil consumption behavior during ramp transients in load by combining oil consumption measurements, in-cylinder measurements, and computer-based modeling. A sulfur based oil consumption method was used to measure real-time oil consumption during ramp transients in load at constant speed in a production spark ignition engine. Additionally in-cylinder liquid oil behavior along the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique.
Technical Paper

Combustion Chamber Deposit Effects on Hydrocarbon Emissions from a Spark-Ignition Engine

A dynamometer-mounted four-cylinder Saturn engine was used to accumulate combustion chamber deposits (CCD), using an additized fuel. During each deposit accumulation test, the HC emissions were continuously measured. The deposit thickness at the center of the piston was measured at the beginning of each day. After the 50 and 35-hour tests, HC emissions were measured with isooctane, benzene, toluene, and xylene, with the deposited engine, and again after the deposits had been cleaned from the engine. The HC emissions showed a rapid rise in the first 10 to 15 hours and stabilization after about 25 hours of deposit accumulation. The HC increase due to CCD accumulation accounted for 10 to 20% of the total engine-out HC emissions from the deposit build-up fuel and 10 to 30% from benzene, isooctane, toluene, and xylene, making CCDs a significant HC emissions source from this engine. The HC emissions stabilized long before the deposit thickness.
Technical Paper

Combustion Characterization in a Direct-Injection Stratified-Charge Engine and Implications on Hydrocarbon Emissions

An experimental study was conducted on a direct-injection stratified-charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System and operated with gasoline. Analysis of the injected fuel flow and the heat release showed that the combustion process was characterized by three distinct phases: fuel injection and distribution around the piston bowl, flame propagation through the stratified fuel-air mixture, and mixing-controlled burn-out with the heat-release rate proportional to the amount of unburned fuel in the combustion chamber. This characterization was consistent with previous visualization studies conducted on rapid-compression machines with similar configurations. Experiments with varied injection timing, spark plug location, and spark timing showed that the combustion timing relative to injection was critical to the hydrocarbon emissions from the engine.
Technical Paper

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

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

Effects of Oxygenated Fuels on DI Diesel Combustion and Emissions

Experiments to study the effects of oxygenated fuels on emissions and combustion were performed in a single-cylinder direct-injection (DI) diesel engine. A matrix of oxygen containing fuels assessed the impact of weight percent oxygen content, oxygenate chemical structure, and oxygenate volatility on emissions. Several oxygenated chemicals were blended with an ultra-low sulfur diesel fuel and evaluated at an equivalent energy release and combustion phasing. Additional experiments investigated the effectiveness of oxygenated fuels at a different engine load, a matched fuel/air equivalence ratio, and blended with a diesel fuel from the Fischer-Tropsch process. Interactions between emissions and critical engine operating parameters were also quantified. A scanning mobility particle sizer (SMPS) was used to evaluate particle size distributions, in addition to particulate matter (PM) filter and oxides of nitrogen (NOx) measurements.
Technical Paper

Effects of Piston-Ring Dynamics on Ring/Groove Wear and Oil Consumption in a Diesel Engine

The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.
Journal Article

Effects of Secondary Air Injection During Cold Start of SI Engines

An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.
Technical Paper

Effects of Substantial Spark Retard on SI Engine Combustion and Hydrocarbon Emissions

Experiments were conducted to determine the effects of substantial spark retard on combustion, hydrocarbon (HC) emissions, and exhaust temperature, under cold engine conditions. A single-cylinder research engine was operated at 20° C fluid temperatures for various spark timings and relative air/fuel ratios. Combustion stability was observed to decrease as the phasing of the 50% mass fraction burned (MFB) occurred later in the expansion stroke. A thermodynamic burn rate analysis indicated combustion was complete at exhaust valve opening with -20° before top dead center (BTDC) spark timings. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the exhaust runner. Time-resolved HC concentrations measured in the port and runner were mass weighted to obtain an exhaust HC mass flow rate. Results were compared to time averaged well downstream HC levels.
Technical Paper

Engine Knock Characteristics at the Audible Level

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

Experimental and Theoretical Analysis of Wankel Engine Performance

A model for predicting the performance and emissions characteristics of Wankel engines has been developed and tested. Each chamber is treated as an open thermodynamic system and the effects of turbulent flame propagation, quench layer formation, gas motion, heat transfer and seal leakage are included. The experimental tests were carried out on a Toyo Kogyo 12B engine under both motoring and firing conditions and values for the effective seal leakage area and turbulent heat transfer coefficient were deduced. The agreement between the predicted and measured performances was reasonable. Parametric studies of the effects of reductions in seal leakage and heat transfer were carried out and the results are presented.
Technical Paper

Fast Gas Temperature Measurement by Velocity of Sound for IC Engine Applications

In the study of internal combustion engines, gas temperatures within the system are of significant importance. The adverse conditions under firing operation, however, make measurements by any means very difficult. This current study seems to have gone the farthest to date for velocity of sound gas temperature measurements in internal combustion engine applications. An ultrasound signal is sent by a transmitting transducer, through the gas medium, and into the receiving transducer. The received signal is recorded, and the gas temperature determined from the time of flight. In-cylinder and exhaust manifold gas temperatures under fired conditions are presented, and are all consistent. Impacts of operating parameters like mixture equivalence ratio and coolant temperature are investigated.
Technical Paper

Flow in the Piston-Cylinder-Ring Crevices of a Spark-Ignition Engine: Effect on Hydrocarbon Emissions, Efficiency and Power

The flow into and out of the piston top-land crevice of a spark-ignition engine has been studied, using a square-cross-section single-cylinder engine with two parallel quartz glass walls which permit optical access to the entire cylinder volume. Schlieren short-time exposure photographs and high speed movies were used to define the essential features of this flow. The top-land crevice and the regions behind and between the rings consist of volumes connected through the ring gaps. A system model of volumes and orifices was therefore developed and used to predict the flow into and out of the crevice regions between the piston, piston rings and cylinder wall.
Technical Paper

Mixture Preparation Mechanisms in a Port Fuel Injected Engine

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

Modeling the Dynamics and Lubrication of Three Piece Oil Control Rings in Internal Combustion Engines

The oil control ring is the most critical component for oil consumption and friction from the piston system in internal combustion engines. Three-piece oil control rings are widely used in Spark Ignition (SI) engines. However, the dynamics and lubrication of three piece oil control rings have not been thoroughly studied from the theoretical point of view. In this work, a model was developed to predict side sealing, bore sealing, friction, and asperity contact between rails and groove as well as between rails and the liner in a Three Piece Oil Control Ring (TPOCR). The model couples the axial and twist dynamics of the two rails of TPOCR and the lubrication between two rails and the cylinder bore. Detailed rail/groove and rail/liner interactions were considered. The pressure distribution from oil squeezing and asperity contact between the flanks of the rails and the groove were both considered for rail/groove interaction.