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Technical Paper

On the Influence of Manifold Geometry on Exhaust Noise

1999-05-17
1999-01-1650
The influence of manifold geometry on exhaust noise is studied. First, a linear description of the problem is presented, so that potential relevant factors may be identified. Then a full non-linear simulation is performed, for a simple geometry, in order to check, in more realistic conditions, the ideas obtained from the linear theory. The results indicate that, although some qualitative trends may be obtained from the linear analysis, the role of back-reaction of the manifold on the engine (a non-linear coupling effect) may be determinant.
Technical Paper

Stratified Scavenging Applied to a Small Capacity Two-Stroke Scooter for the Reduction of Fuel Consumption and Emissions

1999-09-28
1999-01-3271
The advantages of high power to density ratio and low manufacturing costs of a two-stroke engine compared to a four-stroke unit make it currently the most widely used engine type for 50cc displacement 2-wheelers. This dominance is threatened by increasingly severe exhaust emissions legislation, forcing manufactures to develop their two-stroke engines to comply with the legislation. This paper describes a simple solution to reduce these harmful emissions in a cost effective manner, for a scooter application. The method of stratified scavenging is achieved by delivering the fuel into the rear transfer passage from a remote mechanical fuel metering device, operated by intake manifold pressure. Air only is delivered into the cylinder from the remaining transfer passages which are directed towards the rear transfer port, thus impeding the fuel from reaching the exhaust during the scavenging process.
Technical Paper

Influence of Mixture Preparation on Combustion and Emissions Inside an SI Engine by Means of Visualization, PIV and IR Thermography During Cold Operating Conditions

1999-10-25
1999-01-3644
The focus of this work was to determine the influence of spray targeting on temperature distributions, combustion progress and unburned hydrocarbon (HC) emissions at cold operating conditions, and to show the capability of model and full engine tests adapted for different measurement techniques. A comprehensive study applying endoscopic visualization, infrared thermography, combustion and emission measurements was carried out in a 4-stroke 4-cylinder 16-valve production engine with intake port injection during different engine operating conditions including injection angle and timing. In addition 2D visualization and PIV measurements were performed in a back-to-back model test section with good optical access to the intake manifold and the combustion chamber. The measurements in both set ups were in good agreement and show that model tests could lead to useful findings for a real engine.
Technical Paper

Optimization of Natural Gas Combustion in Spark-Ignited Engines Through Manipulation of Intake-Flow Configuration

2000-06-19
2000-01-1948
An investigation was performed to try to quantify the relative importance of large-scale mixing and turbulence in a multi-valve spark-ignited automotive engine converted to use natural gas fuel. The role of mixing was examined by comparing single-point versus multi-point combustion performance at several operating conditions. The fuel-air mixture passed through a static mixer prior to entering the intake manifold in the single point case. This configuration was assumed to produce a well-mixed charge entering the combustion chamber. The fuel was delivered just upstream of the intake port in the multi-point configuration. The charge was assumed to be stratified in this case. The results showed a significant degradation in combustion stability and maximum power but little difference in ignition delay and fully-developed burn duration using multi-point injection. The relative role of turbulence was examined by altering the intake-flow configuration to create three levels of inlet swirl.
Technical Paper

The Impacts of Engine Operating Conditions and Fuel Compositions on the Formation of Combustion Chamber Deposits

2000-06-19
2000-01-2025
This study is a continuing effort toward the goal of understanding deposit formation process in a combustion chamber by probing the impacts of engine operating conditions and fuel compositions on the formation of combustion chamber deposits. To facilitate the study, four retrievable deposit sampling probes were used. The engine operating parameters investigated include coolant temperature, spark advance, manifold air pressure (engine load), and fuel-air ratio. As a continuum of previous studies, toluene was used as the base fuel. In addition, CCD-forming tendencies of isooctane and other aromatics with higher boiling points were investigated. Coolant temperature, fuel-air ratio, and boiling point of the fuel have significant impacts on both the amount and the morphology of deposits formed in a combustion chamber. In contrast, spark advance has little impact on either deposit weight or deposit morphology. Manifold pressure has an intermediate impact on CCD.
Technical Paper

A Stochastic Model of the Fuel Injection of the SI Engine

2000-03-06
2000-01-1088
The paper is devoted to the issues of the non-stationary, stochastic analysis of the fuel injection. The aim of the experiment was to obtain data about SI engine operating parameters during operation. The object randomness in sequentially injected combustion engines are investigated. A numerical procedure is designed for the intake manifold mixture preparation to compensate the mixture variations. There are some direct consequences of inherent non-linearities in the basic dynamics of mixture preparation. Compensating for the mixture dynamics (fuel path, air path consisting of intake manifold and wall-wetting dynamics and the oxygen sensor dynamics) performs well only if the statistical properties of the stochastic processes are sufficiently matched. Since this a priori knowledge is hardly accessible in the present case, the authors implemented an experimental procedure.
Technical Paper

Comprehensive Charge-cooler Model for Simulating Gas Dynamics in Engine Manifolds

2000-03-06
2000-01-1264
Charge-coolers have a significant effect on the performance of turbocharged internal combustion engines. For a comprehensive simulation of internal combustion engines fitted with such devices it is important to model the whole of the manifold system. A wave-action model of a charge-cooler boundary is proposed, together with a methodology for predicting the heat transfer coefficient of the device. This approach enables the instantaneous effectiveness of the charge-cooler to be predicted as a function of the mass flow rate through the device.
Technical Paper

On the Validity of Mean Value Engine Models During Transient Operation

2000-03-06
2000-01-1261
Because there are no production-type sensors which are able to measure the flow directly at the intake port, it is becoming common practice to use models of varying complexity to infer the port air mass flow from other measurements. Given the tight requirements of modern air/fuel ratio (AFR) control strategies, the accuracy of these models needs to be better than ever, during steady-state of course (though λ feedback strategies are by design very robust), but mainly during transient operation. This paper describes why conventional models might be inaccurate during engine transients.
Technical Paper

A Nonlinear Wall-Wetting Model for the Complete Operating Region of a Sequential Fuel Injected SI Engine

2000-03-06
2000-01-1260
The wall-wetting dynamics represent a very important subsystem of the air/fuel path of an SI engine. The precise feedforward control of the air/fuel ratio requires a valid model of the wall-wetting dynamics over the whole operating region of the engine. A global wall-wetting model has been developed for a production SPFI gasoline engine. This model is capable of describing the wall-wetting dynamics not only in a fixed operating point, but also for radical changes of the operating point. Its structure specifically allows for model-based compensator design and on-line parameter identification. Earlier, related publications discussed linear model structures. Those models described the dynamics around a fixed operating point only. This paper shows how one global model for the whole operating range can be constructed from a linear model and its parameter range.
Technical Paper

A Computer Code for S.I. Engine Control and Powertrain Simulation

2000-03-06
2000-01-0938
A computer code oriented to S.I. engine control and powertrain simulation is presented. The model, developed in Matlab-Simulink® environment, predicts engine and driveline states, taking into account the dynamics of air and fuel flows into the intake manifold and the transient response of crankshaft, transmission gearing and vehicle. The model, derived from the code O.D.E.C.S. for the optimal design of engine control strategies now in use at Magneti Marelli, is suitable both for simulation analysis and to achieve optimal engine control strategies for minimum consumption with constraints on exhaust emissions and driveability via mathematical programming techniques. The model is structured as an object oriented modular framework and has been tested for simulating powertrain system and control performance with respect to any given transient and control strategy.
Technical Paper

A Model Based Evaluation of Emissions for Manifold Injected SI Engines

2000-03-06
2000-01-0955
A simple model of combustion and pollutant formation has been set up. It is part of an engine simulator to be used for the study of engine control strategies. The calculation of inlet and exhaust phases is performed by an emptying and filling method, based on the knowledge of mean inlet and exhaust conditions. A single zone thermodynamic model has been utilized for the calculation of the combustion phase. The values of the shape factors of heat release patterns have been modeled to take into account air/fuel ratio, EGR, load and turbulence at ignition starting. Crevice storage of unburned mixture has been considered as the dominant mechanism for unburned HC production. A model for mixing and burning of HC inside the cylinder has been proposed. NO is calculated using the three steps Zeldovich approach. The model produces realistic calculations of combustion pressure and pollutants emission at various speed, load, ignition timing and EGR.
Technical Paper

Identification and Validation of an Air Mass Flow Predictor Using a Nonlinear Stochastic State Representation

2000-03-06
2000-01-0935
The control of an optimal combustion requires an estimation of cylinder air mass (mair), and the calculation of the injected fuel mass. However, the low bandwidth of the engine process and the fuel injector impose a 2 Top Dead Center (TDC) predictive computation of mair. The elaboration of an accurate predictor requires the determination of an exact and robust « intake manifold » model. Thus, the model has to be validated and qualified experimentally, even though no mair sensor and no physical model currently exist. From a behavioural model tending toward the real « intake manifold » behaviour, this study describes the determination of a stochastic state model. The non linearity of the process is treated, as well as the « no computation » characteristic of the internal combustion engine map. The numeralization method of the state system respects the real time constraint of the engine (engine speed interval [Niddle; 7000rpm]).
Technical Paper

Redesign of an Exhaust Manifold Outlet Fastener Using Robust Design Techniques

2000-03-06
2000-01-0917
An L16 orthogonal array parameter Design of Experiment (DOE) evaluated six design parameters of the mating thread interface between the exhaust manifold outlet flange and jointing stainless steel fastener. The objective of this study was to identify optimal parameters for the redesign the thread interface by ensuring 100% seating of the fastener into the manifold flange (here after referred to as stud seating). Since the current fastener and manifold outlet flange interface threads do not always achieve the design objectives, due in part to a form of abrasive wear, consideration was given to develop a testing strategy that would quantify the amount of remaining thread engagement for a given stud length. This testing strategy ensured that the control parameters considered in this experiment would reveal main effects and interactions between the stud and tapped hole threads thus providing the necessary parameters for the redesign on the joint threads.
Technical Paper

A Design Strategy for Four Cylinder SI Automotive Engine Exhaust Systems

2000-03-06
2000-01-0913
This paper details results from a research project to study the influence of exhaust port pressure on the gas exchange process in a reciprocating four-stroke engine. To achieve optimum cylinder charging, it was observed that during the exhaust event, the phasing of compression and rarefaction waves in the exhaust port was of critical importance. Discrete periods during the exhaust event were identified within which compression and expansion pressure waves were best phased to enhance cylinder breathing. The pressure wave resonance characteristics of exhaust manifold components were investigated and a method of identifying the most significant pressure wave components arriving in the exhaust port was developed. The novel application of an acoustic model is shown to give rapid identification of the resonance characteristics of manifold pipes.
Technical Paper

Hydrocarbon Emission from Combustion of Mixtures of Natural Gas and Hydrogen Containing Producer Gas in a SI Engine

2001-09-24
2001-01-3532
Engine experiments have been conducted on a gas fueled SI engine. The engine was fueled with natural gas and mixtures of natural gas and hydrogen containing producer gas in order to examine the effect of addition of producer gas on the combustion process and the engine-out emissions. The experiments showed that addition of producer gas decreased the UHC emission at conditions leaner than λ=1.40. The CO emission was increased by addition of producer gas. This was mainly caused by unburned fuel CO from the producer gas. No effect of producer gas on the NOx emission was detected. Formaldehyde, which is suspected to cause odor problems from natural gas fired engine based power plants, was measured using FTIR. The investigation showed that the formaldehyde emission was decreased significantly by addition of producer gas to natural gas.
Technical Paper

Modifying an Intake Manifold to Improve Cylinder-to-Cylinder EGR Distribution in a DI Diesel Engine Using Combined CFD and Engine Experiments

2001-09-24
2001-01-3685
Improved cylinder-to-cylinder distribution of EGR in a 2-L Direct-Injection (DI) Diesel engine has been identified as one enabler to help reach more stringent emission standards. Through a combined effort of modeling, design, and experiment, two manifolds were developed that improve EGR distribution over the original manifold while minimizing design changes to engine components or interfering with the many varied vehicle platform installations. One of the modified manifolds, an elevated EGR entry (EEE) approach, provided a useful improvement over the original design that meet Euro-II emission standards, and has been put into production as it enabled meeting the Euro III emissions requirements a year early. The second revision, the distributed EGR entry (DEE) design, showed potential for further improvement in EGR distribution. This design has two EGR outlets rather than the one used in the original and EEE manifolds, and was first identified by modeling to be a promising concept.
Technical Paper

Effect of Reduced Boost Air Temperature on Knock Limited Brake Mean Effective Pressure (BMEP)

2001-09-24
2001-01-3682
The effect of low temperature intake air on the knock limited brake mean effective pressure (BMEP) in a spark ignited natural gas engine is described in this paper. This work was conducted to demonstrate the feasibility of using the vaporization of liquefied natural gas (LNG) to reduce the intake air temperature of engines operating on LNG fuel. The effect on steady-state emissions and transient response are also reported. Three different intake air temperatures were tested and evaluated as to their impact upon engine performance and gaseous emissions output. The results of these tests are as follows. The reduced intake air temperature allowed for a 30.7% (501 kPa) increase in the knock-limited BMEP (comparing the 10°C (50°F) intake air results with the 54.4°C (130°F) results). Exhaust emissions were recorded at constant BMEP for varying intake air temperatures.
Technical Paper

Close-Coupled Converter Modeling with a Thinwall Substrate for a Gasoline Engine

2001-03-05
2001-01-3806
On a 1.0 liter engine, the underbody standard ceramic converter was replaced by a close-coupled converter with a ceramic thinwall substrate. The goals were to meet future emissions regulations (Euro 3) and to reduce light-off time maintaining engine performance. The design was conducted based on modeling data. Converter back pressure, heat-up, conversion efficiency as well as the converter external temperatures were predicted. The exhaust gas flow velocity was analysed with CFD modeling to check the distribution of the exhaust gas through the manifold geometrie and through the substrate.
Technical Paper

Modelling, Effect and Behaviour of the EGR Venturi in a Heavy-Duty Diesel Engine

2001-10-01
2001-01-3227
The objective of this work is to make an analysis of the behaviour of the venturi in real working conditions. The modelling of the venturi, as well as the experimental and modelled results obtained, will be described. Modelled and measured techniques have been used to realize this work. A new model of the venturi was developed and using this, it is possible to find important instantaneous variables of the venturi. In order to adjust the calculated model, it was necessary to characterise the steady flow test rig of the venturi. In addition, the information obtained from the engine tests has been essential to correctly adjust the model. Therefore, a combination of the information obtained from both the venturi test and from modelled work was necessary in order to understand the behaviour of the venturi installed in an engine. Different tests have been performed on each venturi.
Technical Paper

Development and Validation of a Computational Process for Pass-By Noise Simulation

2001-04-30
2001-01-1561
The Indirect Boundary Element Analysis is employed for developing a computational pass-by noise simulation capability. An inverse analysis algorithm is developed in order to generate the definition of the main noise sources in the numerical model. The individual source models are combined for developing a system model for pass-by noise simulation. The developed numerical techniques are validated through comparison between numerical results and test data for component level and system level analyses. Specifically, the source definition capability is validated by comparing the actual and the computationally reconstructed acoustic field for an engine intake manifold. The overall pass-by noise simulation capability is validated by computing the maximum overall sound pressure level for a vehicle under two separate driving conditions.
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