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This paper describes a novel catalytic oxidation sensor which represents an attempt to realise a practical sensor for on vehicle detection of catalyst efficiency and misfire. Via experimental and modelling approaches, promising characteristics are established, which could mean that an application to the on-vehicle detection of catalyst efficiency and misfire is feasible.

Afterburning of a rich exhaust/air mixture ahead of the catalyst has been shown in earlier papers to offer an effective means of achieving catalyst light-off in very short times. Protection of the catalyst from overheating is an important aspect of systems using EGI, and on board diagnostics will be required to check for proper function of EGI. In this paper, some options for these requirements are discussed, using a high temperature linear thermistor.

A novel mechanical method of achieving a rapid switch between stoichiometric and lean conditions for SI engines is explored. Two and three throttle configurations, a switch strategy which employs a standard intake manifold and an assembly of pipes and throttle(s), are investigated numerically by using a one-dimensional engine simulation program based on the method of characteristics. The results indicate that it is possible to achieve rapid AFR switch without a torque jump, i.e. unperceptible to the driver.

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.

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.

The transport of fuel during cold start in the intake of a port-injected engine has been investigated using a standard engine with very little modification. A fast response FID sampling from the intake manifold is used to measure the instantaneous vapor concentration during the start. At short times after the start, the engine is stopped, and the port under investigation isolated. The engine is then warmed up by passing hot water through it and at the same time is flushed with hot air, in the port and the cylinder. This evaporates the liquid fuel, and by integrating the vapor concentration multiplied by mass flow of the displaced gas, the fuel mass in the isolated port and cylinder is measured. It is shown how the mass of liquid in the port at the time at which the engine is stopped can reliably be related to the concentration measurement. By stopping the engine at different times after the start, detailed accounting of the fuel transport as a function of time since start can be made.

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.

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.

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.

This paper describes a system for knock detection in automobile engines using the spark plug. Operation is based on detection of the effect of the characteristic pressure fluctuations in the cylinder on the conductivity of the slightly ionized combustion gases in the vicinity of the plug gap. A signal processing method is described which gives adequate signal to noise ratio up to high engine speed.

In the study of mixture motion in an I.C. engine it is desirable to observe the development of flow structures at reduced speed, in order to facilitate data capture. In this paper the use of high molecular weight gases to achieve dynamic similarity with real engine operating conditions at very much reduced engine speeds is examined. The general constraints required to achieve full similarity are discussed, as are the implications for the choice of gas mixtures. It is argued that acceptable similarity can be obtained using a common fluorocarbon, and gas flow motions can be tracked using conventional video equipment and large (20 μm) microballoon seeds.

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.

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.

When gas sample is continuously drawn from the cylinder of an internal combustion engine, the sample that appears at the end of the sampling system corresponds to the in-cylinder content sometime ago because of the finite transit time which is a function of the cylinder pressure history. This variable delay causes a dispersion of the sample signal and makes the interpretation of the signal difficult An unsteady flow analysis of a typical sampling system was carried out for selected engine loads and speeds. For typical engine operation, a window in which the delay is approximately constant may be found. This window gets smaller with increase in engine speed, with decrease in load, and with the increase in exit pressure of the sampling system.

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.

The gas velocity through an automotive catalyst has been determined by measuring the time of flight of a pulse of propane injected at the inlet plane of the catalyst. The arrival time at the exit plane was detected by a fast flame ionization detector. By synchronizing and delaying the injection of propane with respect to the engine crankshaft position, the fluctuations of the exhaust gas velocity during the engine cycle were investigated. A number of tests at different engine load and speed points were carried out. The results show a complex velocity/time characteristic, including flow reversals. The technique is shown to be a viable option for flow measurement in this harsh environment.

Recent studies in the USA have revealed that the catalysts (which are universally fitted to gasoline automobiles) are failing in service to an unacceptable extent. Although the reasons for the failures are not completely clear, it seems that misfiring, leading to highly exothermic reaction in the catalyst, may be responsible for the damage. Legislation is to be enacted later in this decade to address this problem by requiring on board diagnostic (OBD) systems which can measure misfire, as well as catalyst hydrocarbon (HC) conversion efficiency. Although some ideas have been suggested for the OBD requirements, no fully satisfactory sensor technology has yet appeared. This paper describes a novel hydrocarbon sensor based on a surface catalysis principle. The fundamental studies reported here have been made with the automobile application in mind. A catalytic chemi-ionisation model is proposed in order to enhance our understanding of this surface ionisation.