Showing papers on "Spark-ignition engine published in 1996"

A Simple Model for Cyclic Variations in a Spark-Ignition Engine

Abstract: We propose a simple model that explains important characteristics of cyclic combustion variations in spark-ignited engines. A key model feature is the interaction between stochastic, small-scale fluctuations in engine parameters and nonlinear deterministic coupling between successive engine cycles. Prior-cycle effects are produced by residual cylinder gas which alters mean in-cylinder equivalence ratio and subsequent combustion efficiency. The model`s simplicity allows rapid simulation of thousands of engine cycles, permitting in-depth statistical studies. Additional mechanisms for stochastic and prior-cycle effects can be added to evaluate their impact on overall engine performance. We find good agreement with experimental data.

A Study of Combustion of Hydrogen-Enriched Gasoline in a Spark Ignition Engine

Abstract: An investigation has been done on the influence of small amounts of hydrogen added to hydrocarbons-air mixtures on combustion characteristics. The effect of hydrogen addition to a hydrocarbon-air mixture was firstly approached in an experimental bomb, to measure the laminar burning velocity and the shift of lean flammability limit. Experiments carried out with a single-cylinder four stroke SI engine confirmed the possibility of expanding the combustion stability limit, which correlates well with the general trend of enhancing the rate of combustion. An increase of brake thermal efficiency has been obtained with a reduction of HC emissions; the NO{sub x} emissions were higher, except for very lean mixtures.

Cycle-by-Cycle Variations in Spark Ignition Engine Combustion - Part II: Modelling of Flame Kernel Displacements as a Cause of Cycle-by-Cycle Variations

Abstract: A review of cycle-by-cycle variations in combustion and early flame histories is used to discuss the origins of cyclic variations in spark ignition engines. The hypothesis that cyclic variations are caused by the displacement of the flame kernel, is tested by means of a phenomenological turbulent entrainment combustion model. The model results are compared with experimental cycle-by-cycle combustion data, from a range of operating conditions that covers changes in: fuel, air fuel mixture, ignition timing and throttle setting. The combustion is characterized by the cycle-by-cycle variations in: the indicated mean effective pressure, the maximum pressure, the maximum rate of pressure rise, the burn rate and the flame speed. The model predicts correctly the effect of changes in the engine operating point on the cycle-by-cycle variations in combustion, and in many cases there is also good numerical agreement. This study concludes that displacement of the flame kernel during the early stages of combustion, has a major part in the origination of cycle-by-cycle variations in combustion.

An Investigation of Lean Combustion in a Natural Gas-Fueled Spark-Ignited Engine

Abstract: Natural gas has been used extensively as an engine fuel in gas pipeline transmission applications and, more recently, as a fuel for transportation applications including both light-duty and heavy-duty vehicles. The objective of this work was to investigate the performance and emission characteristics of natural gas in an original equipment manufacturer (OEM), light-duty, spark-ignited engine being operated in the lean fueling regime and compare the operation with gasoline fueling cases. Data were acquired for several operating conditions of speed, throttle position, air-fuel equivalence ratio, and spark timing for both fuels. Results showed that for stoichiometric fueling, with a naturally aspirated engine, a power loss of 10 to 15 percent can be expected for natural gas over gasoline fueling. For lean operation, however, power increases can be expected for equivalence ratios below about Φ = 0.80 with natural gas fueling as compared to gasoline. Higher brake thermal efficiencies can also be expected with natural gas fueling with maximum brake torque (MBT) timings over the range of equivalence ratios investigated in this work. Coefficient of variation (COV) data based on the indicated mean effective pressure (IMEP) demonstrated that the engine is much less sensitive to equivalence ratio leaning for natural gas fueling as compared to gasoline cases. The lean limit for a COV of 10 percent was about Φ = 0.72 for gasoline and Φ = 0.63 for natural gas. Lean fueling resulted in significantly reduced NO x levels where a lower plateau for NO x concentrations was reached at Φ near or below 0. 70, which corresponded to about 220 ppm. For natural gas fueling, this corresponded to about 1.21 gm/(kW-h). Finally, with MBT timings, relatively short heat release durations were obtained for lean fueling with natural gas compared to gasoline.

Cycle-by-Cycle Variations in Spark Ignition Engine Combustion - Part I: Flame Speed and Combustion Measurements and a Simplified Turbulent Combustion Model

Abstract: A phenomenological model of turbulent combustion has been developed and validated against data from wide ranging tests on a Ricardo E6 engine. Most tests used iso-octane, with a range of air fuel ratios and ignition timings, for tests at full throttle (with and without knock) and at part throttle. Some full throttle tests were also conducted with methanol and toluene. The engine performance was characterized by mean and coefficient of variation (CoV) of: the peak pressure, the maximum rate of pressure rise, the IMEP, the burn rate and flame speed measurements. The results have been used to argue that the cycle-by-cycle variations in combustion should be characterized by the CoV of IMEP in preference to the CoV of the maximum cylinder pressure. Evidence is also presented to support the observation that the cycle-by-cycle variations in combustion are lower when the early combustion is more rapid. It has also been shown that the CoV of IMEP is a minimum in the region of MBT ignition timing. The phenomenological model of turbulent combustion has given good agreement with the experimental observations of the mean combustion parameters. The tests with methanol and toluene showed slight differences to iso-octane, but smaller changes than thosemore » attributable to a 0.1 change in equivalence ratio. When methanol was used there was a somewhat higher IMEP and slightly faster combustion.« less

Cylinder Pressure in a Spark-Ignition Engine: A Computational Model

Abstract: both valves are open. During this period, the model used an s-curve to describe the gradual transition between exhaust pressure and intake or inlet pressure. The start of compression , which marks the end of the intake process, does not necessarily occur at the same time as the close of the intake valve (IVC). The intake valve closes after bottom center (BC) while the volume in the cylinder is decreasing. The engine speed determines the point at which the fuel/air mixture stops flowing into the cylinder. At lower revolutions per minute (rpm), the start of compression is closer to IVC; at higher speeds, it is closer to BC. An s-curve approximates the angle of the start of compression as a function of engine speed. The volume of the cylinder during intake increases as the piston descends, thereby drawing in the fuel mixture. There is little resistance to gas flow into the cylinder, which causes the pressure in the cylinder to remain relatively constant and equal to the inlet pressure. Compression. Both the intake and exhaust valves are closed during the compression stroke so that the gases can neither enter nor exit the cylinder. The piston is moving upward , so cylinder volume decreases. Pressure increases as the gas in the cylinder is compressed. Because of the high speed of the piston, the duration of compression is short and negligible heat is lost to the walls of the cylinder. Relatively little energy is dissipated due to internal friction of the gas. Overall, there is little change in entropy during compression , and the gas behavior can be described by the equation: 2 (1) This equation allowed for calculation of the cylinder pressure at any crank angle during compression based on the knowledge of initial pressure and volume, P 0 and V 0 , which determine the constant. The volume of the cylinder is a direct function of crank angle, cylinder geometries, crank radius and connecting rod length (see ref. 1). The ratio of the specific heat of the fuel at constant pressure to the specific heat at constant volume is γ; its value varies from compression to combustion to expansion. During compression, γ is approximately equal to 1.3. 3 Combustion. The combustion process was described by the McCuiston, Lavoie and Kauffman (MLK) model. 4 The mass-burn fraction, χ b , was modeled as a function of pressures and volumes: (2) where …

Integrated fiber optic combustion pressure sensor

Abstract: An optical pressure sensor assembly integrated with a spark plug (16) and spark plug boot (12). The pressure sensor comprises an optical fiber (34) with a pressure diaphragm (36) at the tip to sense pressure and pressure changes within the combustion chamber (32) of a spark ignition engine. A channel (30) is provided in the spark plug to hold the sensor. The diaphragm (36) of the sensor is located closer to the spark electrode than to the electric conductor which is encased by the boot (12). The optical fiber (34) is contained within a shaft that is routed through the boot (12) and into the channel (30). The optical fiber (34) is operatively and electrically connected to the vehicle's engine controller. The opto-electric connection to the vehicle's engine controller is made adjacent a coil (72) in the boot (12) or removed from the coil (72). The fiber (34) is surrounded by a nonmetallic shaft (22) outside the engine. Inside the spark plug (16), the shaft is metallic.

ODECS -- A computer code for the optimal design of S.I. engine control strategies

Abstract: The computer code ODECS (Optimal Design of Engine Control Strategies) for the design of Spark Ignition engine control strategies is presented. This code has been developed starting from the author`s activity in this field, availing of some original contributions about engine stochastic optimization and dynamical models. This code has a modular structure and is composed of a user interface for the definition, the execution and the analysis of different computations performed with 4 independent modules. These modules allow the following calculations: (1) definition of the engine mathematical model from steady-state experimental data; (2) engine cycle test trajectory corresponding to a vehicle transient simulation test such as ECE15 or FTP drive test schedule; (3) evaluation of the optimal engine control maps with a steady-state approach; (4) engine dynamic cycle simulation and optimization of static control maps and/or dynamic compensation strategies, taking into account dynamical effects due to the unsteady fluxes of air and fuel and the influences of combustion chamber wall thermal inertia on fuel consumption and emissions. Moreover, in the last two modules it is possible to account for errors generated by a non-deterministic behavior of sensors and actuators and the related influences on global engine performances, and compute robustmore » strategies, less sensitive to stochastic effects. In the paper the four models are described together with significant results corresponding to the simulation and the calculation of optimal control strategies for dynamic transient tests.« less

An Investigation of the Lean Operational Limits of Gas-Fueled Spark Ignition Engines

Abstract: Examination is made of the operational limits in two variable compression-ratio single-cylinder engines when operating on the gaseous fuels methane, propane, LPG, and hydrogen under a wide range of conditions. Two definitions for the limits were employed. The first was associated with the first detectable misfire on leaning the mixture, while the second was the first detectable firing under motoring condition in the presence of a spark when the mixture was being enriched slowly. Attempts were also made to relate these limits to the corresponding values for quiescent conditions reckoned on the basis of the flammability limits evaluated at the mean temperature and pressure prevailing within the cylinder charge at the time of the spark. The measured limits in the engine were always higher than the corresponding flammability. limit values for the three fuels. Both of these limits appear to correlate reasonably well with the calculated mean temperature of the mixture at the time of passing the spark.

Premixed combustion modelling for spark-ignition engine applications

Abstract: A new modelling approach for premixed turbulent combustion has been developed and implemented in computing flow and combustion in axisymmetric engine cylinders. Turbulent transport is treated using a standard second-moment closure model based on Favre density-weighted averaging and the turbulent reaction rate is modelled using a novel laminar flamelet approach. The numerical method is based upon a modified PISO algorithm incorporating second-order bounded spatial differencing. The need for high numerical accuracy is investigated and quantified with reference to engine combustion calculations. The new model for the mean turbulent reaction rate is shown to capture correctly the qualitative behaviour of the flame near to a solid wall, in marked contrast to many existing models. The superiority of the second-moment turbulence model is demonstrated by direct comparison with a standard eddy-viscosity model using an engine combustion test case. A parametric study is carried out to examine the dependence of modelled engine performance on various parameters such as turbulence intensity, compression ratio, engine speed and ignition timing. In every case the expected behaviour is qualitatively well reproduced. © 1996 Society of Automotive Engineers, Inc.

Applications of net-shape molded carbon-carbon composites in IC engines

Abstract: Unique thermal and mechanical properties of carbon-carbon (C-C) composites make them suitable for internal combustion (IC) engine applications. However, the current high manufacturing cost of C-C composites greatly limits their commercial applications. Recent advances in C-C composites manufacturing technologies offer a potentially low cost ($50/lb) material. Thus, forming technologies become the critical factor controlling the application of low cost C-C composites in IC engines. This paper demonstrates the feasibility of using low-cost, molded C-C composites in spark ignition engine applications such as pistons and valves. Problem areas in IC applications of C-C composites are addressed together with a cost estimate to produce C-C pistons at high volume.

Effect of Early-Closing of Intake-Valve on the Engine Performance in a Spark-Ignition Engine

Abstract: In this paper we present the first stage of a study on the effect of early-closing of intake-valve on the engine performance in a spark-ignition engine. A four-valve single-cylinder engine was used with several values of expansion ratio and a half early-closing intake cam. The half early closing leads to almost a half of the volumetric efficiency and the BMEP for all cases of the expansion ratio. It can realize an improvement of about 7% in thermal efficiency under WOT, and about 4% under partial load of BMEP=0.2 MPa. These beneficial results are considered to be mainly caused by the effect of the more-expansion. The ratio of expansion to compression ratios was estimated to be around. 1.4 on the basis of motoring pressure analyses. Under the early-closing condition, an increase in the residual gas fraction was suggested and verified by a heat release analysis using a two-zone combustion model.

An experimental study on quenching crevice widths in the combustion chamber of a spark-ignition engine

Abstract: Hydrocarbon (HC) emissions from spark-ignition engines are now a major environmental problem in many cities of the world. It is difficult to reduce HC emissions during engine warm-up because the catalysts do not work well at low temperatures. The sources of unburned HCs from spark-ignition engines seem to be crevices in the combustion chamber, oil layer, deposits, and quench layer on the cylinder wall surfaces. Single-surface and two-surface flame quenching (crevice) play a large role in generating unburned HCs. Two-surface flame quenching distances (quenching crevice width) in the combustion chamber of a sparkignition engine were investigated using an ion probe capable of detecting flame arrival at a narrow width. The crevice width could be controlled precisely. Because engine combustion has cycle-by-cycle fluctuations, quenching crevice widths were estimated by the statistical analysis. It was defined as the width when the ion detector could detect flame arrival in 50 of 100 cycles. The effects of the mixture equivalence ratio, exhaust gas recycle (EGR) rate, ignition timing, charging efficiency, and combustion chamber wall temperature on the quenching crevice width were investigated. HC emissions in the exhaust port, cycle-by-cycle combustion fluctuation, and temperature of a quenching plate of the ion probe in the combustion chamber were also estimated in the experiments. The quenching crevice width was relatively uniform at the surface of the combustion chamber except in the area close to the ignition spark plug and end gas. The quenching crevice width increased with leaner mixture ratio, larger EGR rate, lower charging efficiency, greater ignition timing, and lower wall temperature.

An Investigation on Simulation Models and Reduction Methods of Unburned Hydrocarbon Emissions in Spark Ignition Engines

Abstract: In this paper, the formation mechanisms of unburned hydrocarbons in the cylinder of spark ignition engine are investigated and the prediction model of unburned hydrocarbon formation and desorption in top land crevice, in the layers of lubricating oil on the cylinder liner and in deposits on the combustion chamber in spark ignition engines are established. The effects of different top land crevice widths, engine speeds, air fuel ratios and spark advance angles on engine exhaust unburned hydrocarbons are investigated. It is shown that the optimum width of engine top land crevice is 0.32 mm (1.3 times of the two wall quenching distance), thus the flame can get into the bottom of crevice and burns out all of the accumulated unburned hydrocarbons in it, consequently the engine exhaust hydrocarbons can be greatly reduce by 35∼50% and with less penalty on engine power output and fuel economy 0.5 ∼ 1.5% loss in power output and 1 ∼ 3% loss in fuel economy), the predicting values by the models match well with the ...

The Effects of Electrode Design on Mixture Ignitability

Abstract: The ignitability of an air/fuel mixture by a spark plug is crucial for spark ignition engine performance, especially at idle and lean fuel conditions. It has been demonstrated that electrode geometry plays an important role in mixture ignitability. Typical industry practice for comparison of a mixture`s ignitability by a spark plug is measured by the coefficient of variance (COV) of the indicated mean effective pressure (MEP). However, the COV of IMEP is influenced by many other factors. Often the COV of IMEP fails to identify the influence of different electrode geometries on mixture ignitability, which hinders the determination of an optimal electrode design. This paper makes use of the 2% mass burn duration and location (when the spark timing is known) to gage mixture ignitability by a spark plug. Using this parameter, results obtained are consistent with the COV of IMEP. The differences between electrode designs are more clearly shown in the difference of 2% mass burn duration than the difference of COV of IMEP. Based on the 2% mass burned duration and location, the ignitability of a mixture by spark plugs with different electrode geometries are compared. By making use of this parameter, the authors are able to identifymore » improved electrode geometry for future spark plug design.« less

Exhaust line of a spark ignition engine

Abstract: Exhaust gas line of an Otto engine comprises: (a) an exhaust gas pipe line (6); (b) a 3-way oxidn. catalyst (14) regulated by a lambda probe; and (c) a reducing catalyst, a so-called SCR catalyst (10) for reducing NOx. The novelty is that the SCR catalyst (10) is arranged in a bypass pipe (7) running parallel to the exhaust gas pipe line (6) between the lambda probe (4) and the oxidn. catalyst (14). The bypass pipe (7) or the exhaust gas pipe line (6) is regulated by an exhaust gas valve (8,9) depending on the engine parameters.

Effect of Top Land Width and Engine Operating Conditions on Exhaust Hydrocarbon Emissions from a Spark Ignition Engine

Abstract: In this paper, the formation mechanisms of unburnt hydrocarbons in the cylinder of a spark ignition engine are investigated and the effects of various top land crevice widths, engine speeds, air-fuel ratios and spark advance angles on engine exhaust hydrocarbons are investigated. The effects of engine top land crevice width on power output and fuel economy are also analysed. It is shown that the optimum engine top land crevice width is 0.32 mm (1.3 times the two surface quench distances), thus the flame can get into the bottom of the crevice and burns out all of the accumulated unburnt hydrocarbons in it, consequently the engine exhaust hydrocarbons can be greatly reduced by 35-50 per cent with less penalty on engine power output and fuel economy (0.5-1.5 per cent loss in power output and 1 ∼ 3 per cent increase in fuel economy).