Search Results

In the application of direct fuel injection to an SI engine the fuel spray characteristics such as droplets velocity and diameter, as well as the penetration length in the combustion chamber - but especially their variation with engine speed and injected quantity - are determining criteria for a mixture formation with the required quality. These characteristics are of particular importance for high speed engines because of the large range of speed variation and become stringent for high speed two-stroke engines where a very short mixture formation time is imposed.

The inherent drastic reduction of CO2, additionally to the limitation of pollutant emission, but at high level of propulsion power and torque as conditions of customer acceptance, imposes the introduction of new concepts of propulsion generation and management. A drastic reduction of CO2 - as cumulated quantity in the atmosphere - is possible by both reduction of specific energy consumption well-to-wheel for propulsion as well as by the utilization of regenerative fuels, ensuring a significant recycling of CO2 emissions from propulsion systems by photosynthesis. Alternative scenarios to the classical automobile propulsion by piston engine show remarkable potentials in terms of power characteristic, energy consumption or pollutant emissions. On the other hand, the development of internal combustion engines is moving from sophisticated mechanics to modular and adaptable process management.

The potential of fuel direct injection regarding the performances of a SI engine is transformable in significant advantages only by an accurate control of the internal air/fuel mixture formation. A main control element is the adaptability of the injection law, respectively of the spray characteristics to the thermodynamic conditions within the combustion chamber for different load and speed. This paper presents a method for the effective implementation of GDI techniques to SI engines, which is exemplified by a system with injection law modulation by pressure. The method is based of the interactive optimization of the processes within the combustion chamber respectively within the injection system, by a feed-back strategy between separate numerical simulations of both systems. For both modules the calibration is ensured by appropriate experimental analysis.

The extremely advantageous power-to-weight, respectively power-to-bulk ratio of two-stroke engines in comparison with four-stroke engines are determining arguments for their further application in light powered two-wheelers. On the other hand, the disadvantages of actual two-stroke engines regarding high pollutant emission, respectively high bsfc - in conditions of the drastic limitation of the pollutant level in the next years - will hinder such applications, if a new quality of the two-stroke process cannot be achieved. As demonstrates in numerous research works, the scavenging improvement of a two-stroke engine can lead to a restricted amelioration of these values, but not to another level. The gasoline direct injection is considered to have the highest potential for such development.

The hydrocarbon emission of a two-stroke engine can be partially decreased by scavenging improvement, but emission levels of a four-stroke engine can be achieved only by changing the mixture formation concept, specifically excluding the fuel from the scavenging process. Numerous research projects of gasoline direct injection - from liquid injection to air assisted systems - have been concentrated on two-stroke engines, determining the selection of the concepts which are suitable for series applications. This paper presents such a concept, based on the ram tuned injection: The system is characterized by a pressure modulation which can be adapted for an appropriate injection law, determining a suitable mixture formation for an engine with specific features. This electronically controlled injection system has been developed as a compact low cost unit for application to two-stroke engines with swept volumes of 50 cm3 and 125 cm3 which equip the two-wheeled vehicles.

The propulsion of future motorcycles and small vehicles will be determined by the reduction of dimensions, weight, fuel consumption and pollutant emission for a considered power output, implicating an improved control of the internal process stages consisting on scavenging, mixture formation and combustion. A main support of such process improvement is the internal mixture formation by gasoline direct injection. However, the compactness and the high-speed range of a small engine for two-wheelers, marine or garden equipment make the application of direct injection more difficult than for automotive engines. On the other hand, after the initially tested wall- and air- guided techniques, it is generally recognized that the only way for a successful large scale utilization of gasoline direct injection is the spray-guided mixture formation.