Refine Your Search


Search Results

Technical Paper

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

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.
Technical Paper

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

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

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

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

UEGO Based Measurement of EGR Rate and Residual Gas Fraction

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

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

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

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

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.
Journal Article

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

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.
Journal Article

A Detailed Chemistry Multi-cycle Simulation of a Gasoline Fueled HCCI Engine Operated with NVO

A previously developed Stochastic Reactor Model (SRM) is used to simulate combustion in a four cylinder in-line four-stroke naturally aspirated direct injection Spark Ignition (SI) engine modified to run in Homogeneous Charge Compression Ignition (HCCI) mode with a Negative Valve Overlap (NVO). A portion of the fuel is injected during NVO to increase the cylinder temperature and enable HCCI combustion at a compression ratio of 12:1. The model is coupled with GT-Power, a one-dimensional engine simulation tool used for the open valve portion of the engine cycle. The SRM is used to model in-cylinder mixing, heat transfer and chemistry during the NVO and main combustion. Direct injection is simulated during NVO in order to predict heat release and internal Exhaust Gas Recycle (EGR) composition and mass. The NOx emissions and simulated pressure profiles match experimental data well, including the cyclic fluctuations.
Technical Paper

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

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

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

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.
Technical Paper

A Fast Response Particulate Spectrometer for Combustion Aerosols

Particulate emissions from IC engines associated with transient engine conditions are very important (similar to the legislated gaseous emissions). This is true both during real-world and test cycle driving. This paper describes an instrument for measuring the number of particles, and their spectral weighting, in the 5nm to 1000nm size range, with a time response of 200ms. This is achieved via an electrostatic classification technique, consisting of a diffusion charger followed by a multi-element, constant voltage, classifier. Conversion of the data to other metrics, such as mass, is also described. Results are presented from artificial test aerosols and from light and heavy duty diesel engines on standard test cycles.
Technical Paper

Experimental Investigation of Changing Fuel Path Dynamics in Twin-Independent Variable Camshaft Timing Engines

The effect of a variable camshaft timing (VCT) disturbance on air-to-fuel ratio (AFR) signal is investigated for a twin-independent (TI) VCT engine. Different types of VCT disturbances on AFR signal are investigated. Gaseous fuel experiments are performed in addition to conventional petrol fuel experiments to show that not all the transient VCT disturbances acting on AFR are due to changes in air path dynamics. Experiments show that varying exhaust valve closing (EVC) timing has a significant effect on the air path dynamics and is an important cause of transient AFR deviations. However varying EVC does not affect the fuel puddle significantly. On the other hand varying inlet valve opening (IVO) timing has a strong effect on the fuel puddle size and is also an important cause of transient AFR deviations. Thus for superior transient AFR control in TI-VCT engines, it is essential to model not only the effects of valve timings on air path dynamics but also on the fuel path dynamics.
Technical Paper

Air-to-fuel Ratio Modulation Experiments over a Pd/Rh Three-way Catalyst

The benefits of deliberately modulating air-to-fuel ratio over a three-way catalyst are disputed. In this work, engine test cell experiments were carried out to assess the performance of a warmed-up Pd/Rh three-way catalyst. The objectives were threefold: first, to determine the best mode of operation; second, to determine if air-to-fuel ratio modulation enhances robustness to transient air-to-fuel ratio disturbances; third, to determine if the conversion efficiency can be manipulated by controlling the shape of the air-to-fuel ratio oscillation. It was observed that the highest conversion efficiency is obtained using a steady air-to-fuel ratio just rich of stoichiometric; however, this mode of operation lacks robustness with respect to transient disturbances and UEGO sensor errors. Robustness can be improved using an oscillating air-to-fuel ratio, but with a sacrifice in peak conversion efficiency.
Technical Paper

The Dynamic Effect of Residual Gas Temperature on Combustion Torque at Idle

The amount of residual gas present in the cylinder has a well documented effect on the combustion event at idle. The high levels of burnt gas present at low engine speed leads to significant cyclic variability. This paper presents research which indicates that the temperature of the residual gas, which can vary from event to event depending on the spark timing, also has a significant effect on the combustion torque. The more the spark timing is retarded from MBT timing, the more thermal energy is present in the exhaust gas. The idle speed control strategy typically varies the spark to give fast torque actuation for good speed regulation and hence the temperature of the residual gas may change significantly within the space of a few events. The paper shows evidence of the phenomenon (with fixed engine speed and air mass flow) and discusses possible causes. It then proceeds to develop a dynamic model for the behaviour.
Technical Paper

Event-Based Mean-Value Modeling of DI Diesel Engines for Controller Design

Models often use time rather than strokes (crank-angle) as the independent variable to describe engine dynamics despite the fact that the dynamics of an internal combustion engine are intrinsically linked to the combustion events. In this paper, two models are developed in parallel in which not only the independent variable is changed but the notion of mass flows as well: flows are in [g/s] for the time-based model and in [g/st] for the event-based model. Both models are of the same computational complexity and show the same accuracy in validation. The investigation of the model properties shows that variations in the flow-related parameters are reduced by a factor of two to five for the event-based model. However, those of the crankshaft dynamics are increased. It is concluded that the model should be chosen in context of the control system to be designed.
Technical Paper

Real Time CO2 Measurement to Determine Transient Intake Gas Composition under EGR Conditions

In a recent paper, a novel fast-response NDIR-based CO2 (fCO2) sensor was described, with applications to automotive engine gas analysis. Certain shortcomings were identified with the sensor. The present paper is concerned with the evolution of the sensor towards a mature instrument and an important application: the measurement of Exhaust Gas Recirculation (EGR) rates during rapid transients. The application described concerns transient EGR measurements at unprecedented bandwidths. Essentially, the technique is based on comparing the inlet manifold CO2 concentration with that in the exhaust. Sampling complications caused by the wide range of inlet pressures encountered in the inlet manifold are discussed. A comparison of EGR from the present test is made with those deduced by the engine controller and a standard slow bench instrument. EGR calibration errors are then identified and related to legislated emissions measured with a similar frequency response.
Technical Paper

Observations of Trans-stoichiometric AFR Spikes in UEGO Sensors

This paper presents experimental data showing unexpected transient behaviour in several production universal exhaust gas oxygen (UEGO) sensors. The spike-like transients occur when passing through the stoichiometric point, and are particularly significant when passing from rich to lean. The paper illustrates how the spikes are affected by exhaust gas flow rate, deviation of air-to-fuel ratio (AFR) from stoichiometry, and rate of change of AFR while passing through stoichiometry. The spikes are most sensitive to the rate at which AFR passes through stoichiometry. Brief discussions on possible causes for the spikes, and on undesirable consequences for feedback control applications, are included.
Technical Paper

A Semi-Empirical Model of Fuel Transport in Intake Manifolds of SI Engines and Its Application in Transient Conditions

A semi-empirical model of fuel transport in the intake manifold of spark ignition engines, which assumes a fraction of injected fuel deposits onto the port walls and describes the detailed fuel film phenomena, is proposed. The model is applied in the throttle ramp transients during which both the air and the fuel flow change significantly. The predicted air fuel ratio excursions, engine torque etc, are in good agreement with the experimental data. Also simulated is another kind of transience, which has only an air flow jump, i.e. with fuelling rate constant, when the engine jumps between stoichiometric and lean running. The results are again in satisfactory agreement with experiment.
Technical Paper

Measurement of Residual Gas Fraction using a Fast Response NO Sensor

Two new techniques are introduced for measuring the residual gas fraction in internal combustion engines. Both techniques use a fast chemiluminescent detection (CLD) type NO sensor. The measurement is made in real-time and requires a single misfire of the engine. Development of the techniques revealed several unexpected, but interesting effects; the results obtained show good agreement with existing knowledge.