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Technical Paper

Analysis of a Stratified Charging Concept for High-Performance Two-Stroke Engines

This paper presents the results and conclusions from a conceptual design study for a stratified charging concept. The stratified charging engine has a displacement of 64 cm3 and a four-port design with reed valves at two ports to control the bypass air. During the intake stroke of the engine, bypass air is sucked into the transfer ports to purge the air-fuel mixture present in the ports from the previous stroke back into the crankcase. This fills the transfer ports near the exhaust with pure air at the beginning of the scavenging stroke. During scavenging, the bypass air is ejected in the cylinder, shielding the exhaust against the fresh mixture coming from the ports on the intake side. This allows the hydrocarbon emissions to be reduced by over 40 %. The conceptual design study is based on an analysis of the mixture short-circuiting mechanisms and CFD investigations of the scavenging flow with charge stratification.
Technical Paper

Concepts for Ultra Low Emission Vehicles

To achieve low emission levels, the handicap of the TWC is its light-off characteristic. It achieves a maximum hot efficiency of nearly 100 %, but this requires a temperature in the range of 300 to 450 °C. To improve this time lag after cold start, the TWC needs additional help to reach the targets of future low (LEV) or ultra low emission (ULEV) levels. This paper describes the work on additional devices to reach the ULEV-levels such as: Electrical Heated Catalyst (EHC). Burner Heated Catalyst (BHC) Hydrocarbon Trap (HCT) as external device. Adsorber Coated Substrate (ACS) in the usual converter box. The comparison of these systems was done with a concept car. The low mileage exhaust results demonstrated the principal suitability of all these devices, but there is still much work to be done to meet the ULEV levels with the guaranted durability. The advantages and disadvantages of the systems are discussed, including estimated weight and cost.
Technical Paper

Exhaust Emission Control on the New 500 SL and 500 SL Structure and Mode of Operation

This paper describes the exhaust emission control system designed for the new Mercedes-Benz sports car generation 300 SL and 500 SL, Remarkable features of the catalytic converters are maximum environmental compatibility, i. e. minimum of emission and noise under all driving conditions. By reduced back-pressure, they also contribute greatly to the well known requirements of a sports car: high performance and high torque over the entire engine-speed-range. Apart from an effective exhaust gas aftertreatment, great efforts were made to prevent the formation of pollutants under all driving conditions. This work is done by intelligent motor management consisting of digital spark control, mechanical-electronic injection, variable valve timing and EGR.
Technical Paper

Low Emission Technologies for High-Performance Handheld Outdoor Products

This paper reviews the current and new engine technologies that are suitable to be implemented in light-weight outdoor power equipment that is mostly powered by two-stroke engines. It gives insight in the concerns associated with the improvement of known technologies and highlights trends for future engine developments. Among others, the paper covers ways for the conventional scavenging improvement, catalyst development, low pressure mixture injection, direct fuel injection, stratified scavenging and also four-stroke technology. These concepts are assessed with respect to performance, cost, size and weight. Special emphasis is laid on the research and development of a catalyst concept for high-performance two-strokes and direct fuel injection. The catalyst is one of the easiest and most effective ways for emission reduction. However, measures have to be found to overcome the severe thermal difficulties.
Technical Paper

New Developments in Catalytic Converter Technology as Demonstrated by Mercedes-Benz 300 SL and 300 CE

The new Mercedes-Benz sportscars typify European catalytic converter design trends. Maximum frontal-area for minimum back-pressure and maximum power of the 4-valve engine was the target for the new 300 SL. This was achieved by moving away from conventional design and using a shape of substrate and housing equidistant to the contour of the transmission-tunnel. Great efforts had to be done to give necessary mechanical strength to the system, but as a result there is a big improvement in engine power and catalytic longterm stability. New canning technology, based upon mat, has been utilised for the 300 CE. A lot of engineering ideas were necessary to develop a so-called “high-tech” variant of the mat-canning system, which fulfills all the demands without any defects, especially under European driving conditions. Apart from economy of space, additional advantages of the new converter, compared with wire-mesh systems, include lower external surface temperature and less noise.
Technical Paper

Secondary Air Injection with a New Developed Electrical Blower for Reduced Exhaust Emissions

Secondary air injection after cold start gives two effects for reduced exhaust emissions: An exothermic reaction at the hot exhaust valves occurs, which increases the temperature of the exhaust gas. It gives sufficient air to the catalyst during the cold start fuel enrichment that is necessary to prevent driveability problems. Handicaps for the wide use of air injection include space constraints, weight and price. An electrical air blower was choosen to best satisfy all these requirements. The development steps are described. The result is a three stage radialblower with extremly high revolutions of about 18000 rpm. The system configuration and the outcome are demonstrated on the new C-Class of Mercedes-Benz. The results show emission reductions higher than 50 %, while also satisfying the development goals of noise, volume, weight and cost requirements.