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Journal Article

Diesel Cylinder Charge Properties: Feed-Forward Control and Cycle-by-Cycle Analysis Using an In-Cylinder Gas Sampling System

2011-04-12
2011-01-0709
Common-rail fuel injection systems on modern light-duty diesel engines are effectively able to respond instantaneously to changes in the demanded injection quantity. In contrast, the air-system is subject to significantly slower dynamics, primarily due to filling/emptying effects in the manifolds and turbocharger inertia. The behavior of the air-path in a diesel engine is therefore the main limiting factor in terms of engine-out emissions during transient operation. This paper presents a simple mean-value model for the air-path during throttled operation, which is used to design a feed-forward controller that delivers very rapid changes in the in-cylinder charge properties. The feed-forward control action is validated using a state-of-the-art sampling system that allows true cycle-by-cycle measurement of the in-cylinder CO₂ concentration.
Technical Paper

UEGO Based Measurement of EGR Rate and Residual Gas Fraction

2011-04-12
2011-01-1289
A technique is presented for measuring the exhaust gas recirculation (EGR) and residual gas fraction (RGF) using a fast UEGO-based O₂ measurement of the manifold or in-cylinder gases, and of the exhaust gases. The technique has some advantages over the more common CO₂-based method. In the case of an RGF measurement, fuel interference must be eliminated and special fuelling arrangements are required. It is shown how a UEGO-based measurement, though sensitive to reactive species in the exhaust (such as H₂), as a system reports EGR/RGF rates faithfully. Preliminary tests showed that EGR and RGF measurements using the O₂ approach agreed well with CO₂-based measurements.
Technical Paper

Fast O2 Measurement using Modified UEGO Sensors in the Intake and Exhaust of a Diesel Engine

2013-04-08
2013-01-1051
Recent work has investigated the use of O₂ concentration in the intake manifold as a control variable for diesel engines. It has been recognized as a very good indicator of NOX emissions especially during transient operation, however, much of the work is concentrated on estimating the O₂ concentration as opposed to measuring it. This work investigates Universal Exhaust Gas Oxygen (UEGO) sensors and their potential to be used for such measurements. In previous work it was shown that these sensors can be operated in a controlled pressure environment such that their response time is of the order 10 ms. In this paper, it is shown how the key causes of variation (and therefore potential sources of error) in sensor output, namely, pressure and temperature are largely mitigated by operating the sensors in such an environment. Experiments were undertaken on a representative light-duty diesel engine using modified UEGO sensors in the intake and exhaust system.
Technical Paper

Impact of Lubricant Composition on Low-speed Pre-Ignition

2014-04-01
2014-01-1213
One of the limits on the maximum fuel efficiency benefit to be gained from turbocharged, downsized gasoline engines is the occurrence of pre-ignitions at low engine speed. These pre-ignitions may lead to high pressures and extreme knock (megaknock or superknock) which can cause severe engine damage. Though the mechanism leading to megaknock is not completely resolved, pre-ignitions are thought to arise from local autoignition of areas in the cylinder which are rich in low ignition delay “contaminants” such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI wall impingement).
Journal Article

Measuring the Impact of Engine Oils and Fuels on Low-Speed Pre-Ignition in Downsized Engines

2014-04-01
2014-01-1219
One of the limits on the maximum fuel efficiency benefit to be gained from turbocharged, downsized gasoline engines is the occurrence of low speed pre-ignition (LSPI). LSPI may lead to high pressures and extreme knock (megaknock or superknock) which can cause severe engine damage. Though the mechanism leading to megaknock is not completely resolved, LSPI is thought to arise from local auto-ignition of areas in the cylinder which are rich in low ignition delay “contaminants” such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI wall impingement). This paper describes a method for testing the propensity of different contaminants to cause a local pre-ignition in a gasoline engine. During one cycle, a small amount of contaminant is injected into one cylinder of a 4 cylinder engine.
Technical Paper

Application of Fast Oxygen Sensors for Investigations into Air-Path Dynamics and EGR Distribution in a Diesel Engine

2014-04-01
2014-01-1177
The control of NOX emissions by exhaust gas recirculation (EGR) is of widespread application. However, despite dramatic improvements in all aspects of engine control, the subtle mixing processes that determine the cylinder-to-cylinder distribution of the recirculated gas often results in a mal-distribution that is still an issue for the engine designer and calibrator. In this paper we demonstrate the application of a relatively straightforward technique for the measurement of the absolute and relative dilution quantity in both steady state and transient operation. This was achieved by the use of oxygen sensors based on standard UEGO (universal exhaust gas oxygen) sensors but packaged so as to give good frequency response (∼ 10 ms time constant) and be completely insensitivity to the sample pressure and temperature. Measurements can be made at almost any location of interest, for example exhaust and inlet manifolds as well as EGR path(s), with virtually no flow disturbance.
Journal Article

A Detailed Chemistry Simulation of the SI-HCCI Transition

2010-04-12
2010-01-0574
A Stochastic Reactor Model (SRM) has been used to simulate the transition from Spark Ignition (SI) mode to Homogeneous Charge Compression Ignition (HCCI) mode in a four cylinder in-line four-stroke naturally aspirated direct injection SI engine with cam profile switching. The SRM is coupled with GT-Power, a one-dimensional engine simulation tool used for modelling engine breathing during the open valve portion of the engine cycle, enabling multi-cycle simulations. The model is initially calibrated in both modes using steady state data from SI and HCCI operation. The mode change is achieved by switching the cam profiles and phasing, resulting in a Negative Valve Overlap (NVO), opening the throttle, advancing the spark timing and reducing the fuel mass as well as utilising a pilot injection. Experimental data is presented along with the simulation results.
Technical Paper

Measurement of the Unburnt Gas Temperature in an IC Engine by Means of a Pressure Transducer

2010-05-05
2010-01-1507
A novel method of measuring cylinder gas temperature in an internal combustion engine cylinder is introduced. The physical basis for the technique is that the flow rate through an orifice is a function of the temperature of the gas flowing through the orifice. Using a pressure transducer in the cylinder, and another in a chamber connected to the cylinder via an orifice, it is shown how the cylinder temperature can be determined with useful sensitivity. In this paper the governing equations are derived, which show that the heat transfer characteristics of the chamber are critical to the performance of the system, and that isothermal or adiabatic conditions give the optimum performance. For a typical internal combustion engine, it is found that the pre-compression cylinder temperature is related to the chamber pressure late in the compression process with sensitivity of the order of 0.005 bar/K.
Journal Article

Experimental Investigation of a Control Method for SI-HCCI-SI Transition in a Multi-Cylinder Gasoline Engine

2010-04-12
2010-01-1245
In HCCI engines, the Air/Fuel Ratio (AFR) and Residual Gas Fraction (RGF) are difficult to control during the SI-HCCI-SI transition, and this may result in incomplete combustion and/or high pressure raise rates. As a result, there may be undesirably high engine load fluctuations. The objectives of this work are to further understand this process and develop control methods to minimize these load fluctuations. This paper presents data on instantaneous AFR and RGF measurements, both taken by novel experimental techniques. The data provides an insight into the cyclic AFR and RGF fluctuations during the switch. These results suggest that the relatively slow change in the intake Manifold Air Pressure (MAP) and actuation time of the Variable Valve Timing (VVT) are the main causes of undesired AFR and RGF fluctuations, and hence an unacceptable Net IMEP (NIMEP) fluctuation. We also found large cylinder-to-cylinder AFR variations during the transition.
Technical Paper

A Fast Detailed-Chemistry Modelling Approach for Simulating the SI-HCCI Transition

2010-04-12
2010-01-1241
An established Stochastic Reactor Model (SRM) is used to simulate the transition from Spark Ignition (SI) to Homogeneous Charge Compression Ignition (HCCI) combustion mode in a four-cylinder in-line four-stroke naturally aspirated direct injection SI engine with cam profile switching. The SRM is coupled with GT-Power, a one-dimensional engine simulation tool used for modeling engine breathing during the open valve portion of the engine cycle, enabling multi-cycle simulations. The mode change is achieved by switching the cam profiles and phasing, resulting in a Negative Valve Overlap (NVO), opening the throttle, advancing the spark timing and reducing the fuel mass as well as using a pilot injection. A proven technique for tabulating the model is used to create look-up tables in both SI and HCCI modes. In HCCI mode several tables are required, including tables for the first NVO, transient valve timing NVO, transient valve timing HCCI and steady valve timing HCCI and NVO.
Technical Paper

An Experimental Study on Engine Dynamics Model Based In-Cylinder Pressure Estimation

2012-04-16
2012-01-0896
The information provided by the in-cylinder pressure signal is of great importance for modern engine management systems. The obtained information is implemented to improve the control and diagnostics of the combustion process in order to meet the stringent emission regulations and to improve vehicle reliability and drivability. The work presented in this paper covers the experimental study and proposes a comprehensive and practical solution for the estimation of the in-cylinder pressure from the crankshaft speed fluctuation. Also, the paper emphasizes the feasibility and practicality aspects of the estimation techniques, for the real-time online application. In this study an engine dynamics model based estimation method is proposed. A discrete-time transformed form of a rigid-body crankshaft dynamics model is constructed based on the kinetic energy theorem, as the basis expression for total torque estimation.
Technical Paper

Assessing Boost-Assist Options for Turbocharged Engines Using 1-D Engine Simulation and Model Predictive Control

2012-09-10
2012-01-1735
Delivering acceptable low end torque and good transient response is a significant challenge for all turbocharged engines. As downsized gasoline engines and Diesel engines make up a larger and larger proportion of the light-duty engines entering the market, the issue takes on greater significance. Several schemes have been proposed to improve torque response in highly boosted engines, including the use of electrical assist turbochargers and compressed air assist. In this paper we examine these methods with respect to their effectiveness in improving transient response and their relative performance along with some of the practical considerations for real world application. Results shown in this paper are from 1-D simulations using the Ricardo WAVE software package.
Technical Paper

A Novel System for Reducing Turbo-Lag by Injection of Compressed Gas into the Exhaust Manifold

2013-04-08
2013-01-1310
A key challenge in achieving good transient performance of highly boosted engines is the difficulty of accelerating the turbocharger from low air flow conditions (“turbo lag”). Multi-stage turbocharging, electric turbocharger assistance, electric compressors and hybrid powertrains are helpful in the mitigation of this deficit, but these technologies add significant cost and integration effort. Air-assist systems have the potential to be more cost-effective. Injecting compressed air into the intake manifold has received considerable attention, but the performance improvement offered by this concept is severely constrained by the compressor surge limit. The literature describes many schemes for generating the compressed gas, often involving significant mechanical complexity and/or cost. In this paper we demonstrate a novel exhaust assist system in which a reservoir is charged during braking.
Technical Paper

Investigation into Partially Premixed Combustion in a Light-Duty Multi-Cylinder Diesel Engine Fuelled Gasoline and Diesel with a Mixture of

2007-10-29
2007-01-4058
Partially premixed compression ignition (PPCI) engines operating with a low temperature highly homogeneous charge have been demonstrated previously using conventional diesel fuel. The short ignition delay of conventional diesel fuel requires high fuel injection pressures to achieve adequate premixing along with high levels of EGR (exhaust gas recirculation) to achieve low NOx emissions. Low load operating regions are typified by substantial emissions of CO and HC and there exists an upper operating load limitation due to very high rates of in-cylinder gas pressure rise. In this study mixtures of gasoline and diesel fuel were investigated using a multi-cylinder light duty diesel engine. It was found that an increased proportion of gasoline fuel reduced smoke emissions at higher operating loads through an increase in charge premixing resulting from an increase in ignition delay and higher fuel volatility.
Technical Paper

Residual Gas Fraction Measurement and Estimation on a Homogeneous Charge Compression Ignition Engine Utilizing the Negative Valve Overlap Strategy

2006-10-16
2006-01-3276
This paper is concerned with the Residual Gas Fraction measurement and estimation on a Homogeneous Charge Compression Ignition (HCCI) engine. A novel in-cylinder gas sampling technique was employed to obtain cyclic dynamic measurements of CO2 concentration in the compression stroke and in combination with CO2 concentration measurements in the exhaust stroke, cyclic Residual Gas Fraction was measured. The measurements were compared to estimations from a physical, 4-cylinder, single-zone model of the HCCI cycle and good agreement was found in steady engine running conditions. Some form of oscillating behaviour that HCCI exhibits because of exhaust gas coupling was studied and the model was modified to simulate this behaviour.
Technical Paper

A Simple Diesel Engine Air-Path Model to Predict the Cylinder Charge During Transients: Strategies for Reducing Transient Emissions Spikes

2006-10-16
2006-01-3373
Simple air-path models for modern (VGT/EGR equipped) diesel engines are in common use, and have been reported in the literature. This paper addresses some of the shortcomings of control-oriented models to allow better prediction of the cylinder charge properties. A fast response CO2 analyzer is used to validate the model by comparing the recorded and predicted CO2 concentrations in both the intake port and exhaust manifold of one of the cylinders. Data showing the recorded NOx emissions and exhaust gas opacity during a step change in engine load illustrate the spikes in both NOx and smoke seen during transient conditions. The predicted cylinder charge properties from the model are examined and compared with the measured NOx and opacity. Together, the emissions data and charge properties paint a consistent picture of the phenomena occurring during the transient. Alternative strategies for the fueling and cylinder charge during these load transients are investigated and discussed.
Technical Paper

A Fourier Analysis Based Synthetic Method for In-cylinder Pressure Estimation

2006-10-16
2006-01-3425
The cylinder pressure signal, as an instantaneous and direct measure of the engine operation, contains valuable information for closed loop engine control and offers very useful engine monitoring and control capabilities. The estimation technique for cylinder pressure has been investigated for many years. Based on the Frequency Analysis Method, a synthetic estimation method is proposed in this paper to estimate pressure. Methods that are successful in obtaining a more accurate estimated cylinder pressure over a wider range of crankshaft angle are reported. Quantitative results obtained from application of the method are also given.
Journal Article

Gasoline Fuelled Partially Premixed Compression Ignition in a Light Duty Multi Cylinder Engine: A Study of Low Load and Low Speed Operation

2009-06-15
2009-01-1791
The objective of this study was to examine the operating characteristics of a light duty multi cylinder compression ignition engine with regular gasoline fuel at low engine speed and load. The effects of fuel stratification by means of multiple injections as well as the sensitivity of auto-ignition and burn rate to intake pressure and temperature are presented. The measurements used in this study included gaseous emissions, filter smoke opacity and in-cylinder indicated information. It was found that stable, low emission operation was possible with raised intake manifold pressure and temperature, and that fuel stratification can lead to an increase in stability and a reduced reliance on increased temperature and pressure. It was also found that the auto-ignition delay sensitivity of gasoline to intake temperature and pressure was low within the operating window considered in this study.
Journal Article

Analysis of In-Cylinder Hydrocarbons in a Multi-Cylinder Gasoline HCCI Engine Using Gas Chromatography

2009-11-02
2009-01-2698
Gasoline Homogeneous Charge Compression Ignition (HCCI) combustion has been studied widely in the past decade. However, in HCCI engines using negative valve overlap (NVO), there is still uncertainty as to whether the effect of pilot injection during NVO on the start of combustion is primarily due to heat release of the pilot fuel during NVO or whether it is due to pilot fuel reformation. This paper presents data taken on a 4-cylinder gasoline direct injection, spark ignition/HCCI engine with a dual cam system, capable of recompressing residual gas. Engine in-cylinder samples are extracted at various points during the engine cycle through a high-speed sampling system and directly analysed with a gas chromatograph and flame ionisation detector. Engine parameter sweeps are performed for different pilot injection timings and quantities at a medium load point.
Technical Paper

Highly Homogeneous Compression Ignition in a Direct Injection Diesel Engine Fuelled with Diesel and Biodiesel

2007-07-23
2007-01-2020
Highly homogeneous compression ignition is difficult to achieve in a direct injection diesel engine. The difficulty of achieving adequate fuel vaporization and the problems of fuel spray wall impingement are the main factors. Limitation of the maximum operating load results from high rates of pressure rise that occur in this combustion regime. The levels of HC and CO emissions are raised substantially when compared with conventional combustion and remain a significant emission factor. In this study, two methods of achieving highly homogeneous combustion in a direct injection diesel engine were investigated, Nissan MK type and early injection. The effects of fuel injection pressure, injection timing, EGR level, EGR cooler efficiency and compression ratio were examined using a conventional 4 cylinder 2.0L common rail diesel engine with 18.4:1 and 14.4:1 compression ratios.
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