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A transient one-dimensional model developed to simulate the thermal and conversion characteristics of adiabatic monolithic converters operating under warm-up conditions is presented. The model takes into account the gas-solid heat and mass transfer, axial heat, conduction, chemical reactions and the related heat release. The model has been used to analyze the transient response of an axisymmetric catalytic converter during a warm-up as a function of catalyst design parameters and operating conditions in order to observe their effects on the lightoff behaviour. The experimental test was carried out in two steps: the first on a sample for lightoff test and the second on two-stroke 150 cc engine with Pt/Rh metal-supported catalyst and full open-throttle condition. The simulated temperatures are close to test results. The predicted conversion efficiencies are qualitatively acceptable.

The problems of Two-Stroke SI engines regarding high fuel consumption and unburned hydrocarbon emissions, both caused by the short circuiting of fresh homogeneous mixture during the scavenge process, are well-known. The progress of Piaggio since 1977 in state-of-art direct fuel injection systems, oriented to development of Hi-Tech solutions for 2T SI engines to overcome the above drawbacks, is analyzed. The analysis includes several streams of research ranging from conventional crankcase scavenged engines with direct solid mechanically controlled fuel injection to solutions with separate scavenging pump with electronically controlled injection units, and from low pressure injectors to air-assisted fuel injection with stratified charge. Each solution is examined with presentation of typical engine parameters and cost data.

Following general remarks about high pressure direct injection systems impact on two stroke S.I. engine applications, further advantages, both on emissions as well as fuel consumption, obtainable with a variable timing injection system are presented. An exhaustive evaluation, carried out on a single cylinder air cooled engine, clearly shows that sensible reductions, basically in HC emissions as well as in fuel consumptions can be obtained delaying the injection beginning depending on RPM and engine load. Further advantages appear available at idle, injecting every other cycle, if a suitably conceived system is adopted. Finally an electronically controlled high Pressure injection system, derived from a low cost and dependable solution for small engines is proposed.

The nowadays two-stroke engine technique is directed toward new concepts to reduce fuel consumption and pollution. Typical features are direct injection of fuel and no lost oil lubrication: a separate scavenging system is becoming so a must. Following general consideration about different scavenging pumps, a regenerative blower solution is proposed. Regenerative blowers present in fact several advantages in comparison with other solutions like simplicity in construction and on engine fitting, no maintenance and low cost. An exhaustive experimental evaluation was carried out on a direct injection two-stroke S.I. engine with a separate scavenge, already described in a previous work by one of the authors. The results show the practical feasibility of the proposed solution. In fact, the regenerative blower is suitable to match the engine air breath demand all over its utilization range.

After some general considerations about the extended use of Continuously Variable Transmissions (CVT's) for lightweight vehicles, which clearly show the two-fold advantage, the first of a very simple, compact and well integrated with engine transmission, the second to make possible the calibration of the engine only in a limited operating range, the efficiency of this type of transmission is investigated. A theoretical analysis of CVTs is carried out, in order to identify all the characterizing physical parameters. The design of a specific test rig is then presented. Since the transmission ratio depends on forces equilibrium, the centerline force appears to be the most important characterizing parameter. The new system is particularly conceived for small power output, i.e. minimum friction losses.

The Hi-Tech Two-Stroke SI engine is finding good appreciation in various fields of vehicle application and the final solution appears to include air assisted direct fuel injection and several solutions are now evaluated by the major world engine manufacturers. Those solutions anyway are poorly tailored to be fitted on very small engines such as for moped or light scooter applications both for the complications they require, consequentely the costs, and the difficult tuning of low load and idle caused by the very low quantity of fuel per cycle required. The proposed completely mechanical solution instead does consent with small modifications to the engine, only a new cylinder head is in fact required, to manage very well the engine all over its utilization range. After general considerations of the philosophy of the system and on the main parameters evaluation, a practical application on a 50cc scooter engine is described.

The paper mainly deals with the heat transfer and thermal loading problems faced during the development of an high specific output IDI Diesel engine, suitable for a small van. Boundary conditions and heat transfer coefficients of the engine head were obtained from experimental measurements and a Finite Element Method model was developed to analyze temperature distribution in the head. The results of calculations and experimental tests led to an optimized solution for the cooling system based on air and oil passages in the hottest zone of the head.

Following the state - of - the - art analysis of typical applications of two-stroke SI engines in road vehicles, new solutions for this type of engine are examined. The two-stroke engine appears as an extremely attractive one during part-throttle opera tions especially from the point of view of fuel consumption, when the problems caused by fresh mixture short-circuiting are overcome. This fact is well confirmed by the renewed interest in the two-stroke cycle SI Engine. A new solution, with direct fuel injection and separate scavenging pump, that shows very low fuel consumption data down to very low B.M.E.P. levels while mantaining a high specific power output and acceptable HC emissions, is then presented.

The emission standards compliance is really becoming effective generally for all the class of engines and particularly for two-stroke SI. While for larger capacity and more valuable applications, such as scooters, snowmobiles, marine engines, the state of the art appears consolidated with the use of direct fuel injection systems, the engines dedicated to very light and simple applications need a different approach in terms of simplicity and cost. Aiming in this direction a system including a self - sustained air injection system in the exhaust and oxidation catalysts was prepared. The influence of the main design parameters governing the system performances and their mathematical relationships were experimentally studied with the aid of a DOE (Design of Experiment) technique methodology.

The future urban mobility strategies, especially in cities with high population density, include the individual transportation means as one of the main components to contribute to the solution of the two fundamental problems, namely the traffic concentration and the individual satisfaction. Following the consolidated trend, the 2000's vehicles shall be characterized by extremely reduced environmental impact in terms of pollutant emissions, noise, fuel consumption (low carbon dioxide production). In this sense the two-wheelers appear the most favorable candidate provided that a suitable propulsive unit is available. The present work describes the development of a propulsive unit characterized by a direct injected two-stroke engine with FAST technology, an electronic engine management system and a very efficient CVT transmission.

Following general considerations on the present state of commuter traffic in the downtown sections of the cities, the specifications of an highly efficacious and efficient vehicle for individual transportation are analyzed. A two-wheeler vehicle appears very attractive when pollution and noise are overcome. A new formula of vehicle is so presented looking for a minimum optimun solution to the problem. The basic feature consists in an hybrid propulsion system, namely: internal combustion engine with catalytic muffler for downtown approach and an accumulator powered electric motor during restricted area trips. After the presentation of the experimental results, some considerations on utilization coefficient as well as energy use efficiency, in comparison with other modes of transportation, are presented.

The advantages of air assisted direct fuel injection systems to achieve high atomization degree into the combustion chamber of SI engines are well-known. The solutions up to now proposed appear anyway poorly tailored to be suitable for small engine applications. In fact scaling down such existing systems for automotive applications, they present mainly two drawbacks: the costs and a difficult tuning of the very low quantity of fuel required per cycle. Moreover the amount of electric energy required makes the engines not self-sufficient. To overcome the above mentioned problems, Piaggio has developed a completely mechanical low cost fuel injection system, named FAST (Fully Atomized Stratified Turbulence), which does consent a very atomized and stratified mixture lean combustion process, i.e. a dramatic improvement of emissions and fuel consumption. After general considerations, the application of such system to a small capacity 2T engine is analyzed.

"In the design of new CI engines, it is of paramount importance to reduce the pollutants and fuel consumption," writes author Marco Nuti. In this, the first book devoted entirely to exhaust emissions from two-stroke engines, Nuti examines the technical design issues that will determine how long the two-stroke engine survives into the twenty-first century. Dr. Nuti, director of Technical Innovation at Piaggio, thoroughly explores pollutant formation and control from unburned hydrocarbon emissions, carbon monoxide emissions, catalytic aftertreatment, and secondary air addition.