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A quasi-dimensional computer simulation model is presented to simulate the thermodynamic and chemical processes occurring within a spark ignition engine during compression, combustion and expansion based upon the laws of thermodynamics and the theory of equilibrium. A two-zone combustion model, with a spherically expanding flame front originating from the spark location, is applied. The flame speed is calculated by the application of a turbulent entrainment propagation model. A simplified theory for the prediction of in-cylinder charge motion is proposed which calculates the mean turbulence intensity and scale at any time during the closed cycle. It is then used to describe both heat transfer and turbulent flame propagation. The model has been designed specifically for the two-stroke cycle engine and facilitates seven of the most common combustion chamber geometries. The fundamental theory is nevertheless applicable to any four-stroke cycle engine.

A mathematical model has been developed which predicts the tailpipe exhaust emissions of two-stroke cycle engines utilising an oxidising catalytic converter. This model is currently one-dimensional and has been developed as an aid to the design of engine/exhaust systems. The experimental rig employed has a two-fold function, its primary task was to aid in the validation of the model. Secondary to this it was used to simulate the gaseous properties of the exhaust gas at various positions in the exhaust system. The validation exercise is currently proceeding utilising metallic substrate technology with preliminary results indicating that the model is showing good correlation to measured values.

The results of this paper will show the reader how to quantify a minimum light-off temperature to meet the required emissions standards with the use of a 3-way catalytic converter. The method can be applied to both motorcycle and larger automotive catalysts to help meet their respective emissions standards (Euro 5/Euro 7). The ability to predict a light-off temperature for any catalyst at the beginning of the project saves both time and resource. With an emphasis on how the shape of the light-off curve affects the cumulative tailpipe emissions and how shape of the light-off curves change with the ageing process. Changes in the light-off curves will be reviewed to understand how the chemical reactions and pore diffusion mechanisms within the catalyst deplete to negatively affect performance over its life time.

This study describes an innovative monolith structure designed for applications in automotive catalysis using an advanced manufacturing approach developed at Imperial College London. The production process combines extrusion with phase inversion of a ceramic-polymer-solvent mixture in order to design highly ordered substrate micro-structures that offer improvements in performance, including reduced PGM loading, reduced catalyst ageing and reduced backpressure. This study compares the performance of the novel substrate for CO oxidation against commercially available 400 cpsi and 900 cpsi catalysts using gas concentrations and a flow rate equivalent to those experienced by a full catalyst brick when attached to a vehicle. Due to the novel micro-structure, no washcoat was required for the initial testing and 13 g/ft3 of Pd was deposited directly throughout the substrate structure in the absence of a washcoat.

The improvement in both performance and thermal efficiency of internal combustion engines at higher compression ratios is a well known phenomena. Indeed, a simple Otto Cycle analysis show a potential efficiency improvement of 13% by increasing the compression ratio from 9:1 to 15:1. However, the dilemma for engineers has always been in the realization of a practical operational mechanism. This paper describes the ECCLINK VCR mechanism which enables compression ratio to be altered within given limits on a running engine. A single cylinder 500 cm3 four-stroke research engine, incorporating the ECCLINK mechanism, has been built and tested. Results are presented at both full load and part load over a range of compression ratios, showing improvements in performance and fuel economy. Of particular interest is the fact that full load bsfc improvements equate to typical Otto cycle values.

Accelerated aging of automotive catalysts has become a routine process for the development of new catalytic formulations and for homologation of vehicle emissions. In the standard approach, catalyst samples are subjected to temperatures in excess of 800°C on a predefined test cycle and aged for precise timescales representative of certain vehicle mileage. The high temperature feed gas is traditionally provided by a large gasoline engine but, increasingly, alternative bench-aging techniques are being applied as these offer more precise control and considerable cost savings, as well as offering more development possibilities. In the past few years, emissions control of light duty vehicles has become increasingly prominent as more stringent emissions legislations require more complex after-treatment systems. Aging of the catalysts are not fully understood as they are subjected to many varying environments, including temperature and gas concentrations.

This paper describes an experimental comparison of loop and cross scavenged single-cylinder research engines. The cross scavenged engines have employed the QUB type deflector piston. The initial results show that the QUB cross scavenged engine exhibited inferior performance characteristics. Utilizing the QUB single cycle test rig, a study of the QUB cross scavenging system has shown that the bore-to-stroke ratio significantly influences the scavenging behaviour; reduction of the bore-to-stroke ratio from over-square values gave improved characteristics. On the basis of this finding, a new cross scavenged cylinder barrel was designed. In a subsequent series of dynamometer tests, improvements in power, fuel economy and emission characteristics were recorded for the new cylinder. These improved results approximate closely to those recorded for the loop scavenged engine and are considerably superior to those of the original cross scavenged cylinder.

This paper outlines a novel method employed to accurately age catalysts to the required OBD limit for European motorcycles legalisation Euro 5 using a combination of modelling and testing. The method applies several strategies, including thermal ageing and catalyst poisoning, to reduce catalyst activity in order to mirror real-world catalyst ageing. Predictions were made using a combined global and micro kinetic model to specify catalyst activity to a matching light-off condition. The model simulated a motorcycle operating on a WMTC (World Motorcycle Test Cycle) and adjusted catalyst activity (Precious metal and Oxygen Storage Capacity) until tailpipe emissions matched the limits for Euro 5 OBD II. The same model ran a simulated light-off test to predict the light-off point for the catalyst. The catalyst was then aged to match this light-off performance using a RAT ageing cycle with additional poisoning to reach the target deactivation.

Due to stringent emissions legislation, the use of three way catalysts is becoming increasingly prevalent in motorcycles and scooters. This paper describes the development, and subsequent validation, of a detailed mathematical model for the oxygen storage processes in three-way catalysts. The model consists of several interdependent sub-models describing the oxidation and reduction processes and their interaction with a kinetic model of the catalyst. The structure and equations of the model are detailed and their significance discussed. For the validation phase of the work a purpose-built miniature catalyst test rig has been assembled and a series of experiments conducted to assess the oxygen storage processes. Analysis of this data also provided values for the controlling constants associated with the oxidation and reduction reactions. These results are included and compared with other published data.

With emission legislations becoming ever more stringent there is an increased pressure on the after-treatment systems, and more specifically the three-way catalysts. With recent developments in emission legislations, there is requirement for more complex after-treatment systems and understanding of the aging process. With future legislation introducing independent inspection of emissions at any time under real world driving conditions throughout a vehicle life cycle this is going to increase the focus on understanding catalyst behavior during any likely conditions throughout its lifetime and not just at the beginning and end. In recent years it has become a popular approach to use accelerated aging of the automotive catalysts for the development of new catalytic formulations and for homologation of new vehicle emissions.

With emission legislation becoming ever more stringent, automotive companies are forced to invest heavily into solutions to meet the targets set. To date the most effective way of treating emissions is through the use of catalytic converters. Current testing methods of catalytic converters whether being tested on a vehicle or in a lab reactor can be expensive and offer little information about what is occurring within the catalyst. It is for this reason and the increased price of precious metal that kinetic modeling has become a popular alternative to experimental testing. Many kinetic models and kinetic parameters have appeared in literature in recent years, a comparison of these kinetic parameters for the global reaction of CO oxidation is presented.

The after-treatment of exhaust gas using 3-way catalytic converters is now normal practice in automotive applications. For other applications, such as outboards, motorcycles and utility engines, new legislation is now in place in both Europe and North America. Further reduction of the permitted emission levels require the use of catalysts for two-stroke engine applications. However, current automotive catalyst systems are not suitable for durable operation in most two-stroke engines and new analytical tools are required to aid the development engineers in the implementation of revised designs and operating strategies. This paper reviews the range of modeling techniques which have been developed for automotive uses and presents new and modified models suitable for two-stroke engines. This requires particular emphasis to be placed on the oxidation reactions that predominate in the two-stroke engine exhaust.

With emission legislations becoming ever more stringent, there is an increased pressure on after-treatment systems and more specifically three-way catalysts. With recent developments in emission legislations, there is a requirement for more complex after-treatment systems and understanding of the aging process. Whilst the body of understanding on catalyst deactivation and, in particular, catalyst aging is growing, there are still significant gaps in understanding, particularly how real world variations in temperature, flow rate and gas concentrations affect catalyst behavior. Under normal driving conditions, the catalyst can experience varying oxygen concentrations, such as under heavy acceleration or cruising down a hill will show a variation in oxygen from the engine emissions. The effect that varying oxygen concentrations has on the rate of aging is not fully understood and hence the total deactivation and conversion efficiencies are not known throughout the catalyst lifetime.

A three-way automotive catalyst's ability to store oxygen is still a crucial performance metric for modern day catalyst applications. With more stringent emissions legalisation, the oxygen storage capacity (OSC) within a catalyst can assist with converting different harmful exhaust gases such as CO, THC and NOx under transient operating conditions. Additionally, OSC is currently the only onboard catalyst performance metric recorded during a vehicle's useful life. Catalyst performance is correlated to this OSC measurement. OSC in three-way automotive catalysts can be split into two main OSC types. "Latent" OSC deep within the washcoat and "dynamic" OSC on the surface of the catalyst washcoat. Dynamic OSC is more commonly applied in the evaluation of useful OSC of the catalyst during practical operation.

A Three-way automotive catalyst's ability to store oxygen is still a crucial performance metric for modern day catalyst applications. With more stringent emissions legalisation, the oxygen storage capacity (OSC) within the catalyst can assist with converting different exhaust gases such as CO, THC and NOx under transient operating conditions. OSC is currently the only onboard catalyst performance metric recorded during a vehicle's useful life. Catalyst performance is correlated to this OSC measurement. Rhodium is a precious metal used in automotive catalysts to help with the conversion of NOx. The price of rhodium is increasing drastically, requiring original equipment manufacturers (OEMs) to look at cost-effective alternatives to maintain NOx conversion within the exhaust stream. OSC in the catalyst is possible due to ceria in the washcoat. Stored oxygen can help promote other reactions in the catalyst bed to help with the conversion of NOx.

Understanding the behavior of automotive catalysts formulations under the wide range of conditions characteristic of automotive applications is key to the design of present and future emissions control systems. Platinum-based oxidation catalysts have been in use for some time to treat the exhaust of diesel-powered vehicles and have, as part of an emissions control package, successfully enabled compliance with emissions legislation. However, progressively stringent legislated limits, coupled with the need to reduce vehicle manufacturing costs, is incessantly demanding the development of new and improved catalyst formulations for the removal of pollutants in the diesel exhaust. With the introduction of low sulfur diesel fuel, and the advantageous decline in Palladium prices with respect to Platinum, bimetallic Pt:Pd-based catalysts have found an application in diesel after treatment.

This paper details a theoretical and experimental study of combustion phenomena within a two-stroke cycle, spark ignition engine. The theoretical part of the work involved the development of an improved quasi-dimensional combustion model. This model was incorporated into a computer program which was used to predict the thermodynamic and chemical changes occurring within a two-stroke engine during the closed cycle of the engine. The simulation uses a turbulent kinetic energy model to predict flame front velocity. Combustion chamber geometry is used to estimate entrained mass and mass fraction burned is calculated from a simple eddy-entrainment approach. The experimental work was undertaken to validate the combustion model. Two separate cylinder heads were designed with different combustion chambers and tested on a standard loop-scavenged engine over a range of operating conditions.

An experimental transient catalyst test rig has been developed and used to investigate the location and intensity of the reactions in a two-stroke oxidation catalyst as the inlet temperature is increased from ambient through light-off at a rate which is similar to that found in an engine exhaust after a cold start. The catalyst samples used in this apparatus are relatively large by plug flow reactor standards, (50mm diameter x 70mm long), which allows significant radial and axial variations in temperature and activity to occur. The gas and temperature readings recorded during these tests show that, even though the front face of the catalyst is hotter than the rear due to the transient temperature ramp, the highest reaction rate occurs in the rear half of the catalyst during the early stages of light-off. As the light-off process progresses, the reaction zone moves in a radial direction and migrates towards the front face.

Catalyst aging is presently one of the most important aspects in aftertreatment development, with legislation stating that these systems must be able to meet the relevant emissions legislation up to a specified mileage on the vehicle, typically 150,000 miles. The current industry approach for controlling aging cycles is based solely on the detailed specification of lambda (air-fuel mixture concentration ratio), flow rate and temperature without any limitations on gas mixture. This is purely based upon the experience of engine-based aging and does not take into account any variation due to different engine operation. Although accurate for comparative testing on the same engine/engine type, inconsistencies can be observed across different aging methods, engine types and engine operators largely driven by the capability of the technology used.

Computer simulation is now considered to be a crucial stage in the design of automotive catalysts due to the increasing complexity of modern aftertreatment systems. The resulting models almost invariably include surface reaction kinetics that are measured under controlled conditions similar to those found on a vehicle. Repeatability of the measurements used to infer surface reaction rates is fundamental to the accuracy of the resulting catalyst model. To achieve the required level of repeatability, it is necessary to ensure that the catalyst sample in question is stable and that its activity does not change during the test phase. It is therefore essential that the catalyst has been lightly aged, or "de-greened" before testing begins. It is also known that the state of the catalyst's surface prior to testing has an impact on its subsequent light-off performance and that test history can play an important role in catalyst activity.