Abstract
The development and research works on liquid fuel injection in spark-ignited direct injection (SIDI) engines, apart from so common in recent years simulation methods, still have a significant cognitive substrate. This is related to experimental research on repeatability of combustion process using multi- and mono-cylinder test engines and Rapid Compression Machines. The repeatability of preparation and delivery processes has immediate impact on repeatability of combustion process. Except for the necessity of obtaining the repeatability of fuel amounts, the repeatability of injected fuel spray is required. The penetration range and spray area in combustion chamber have direct impact on mixture creation and formation. The optical research on fuel injection has been made in order to determinate its repeatability. The research on unrepeatability of fuel spray propagation has been conducted using piezoelectric injectors of outward-opening type, being primary elements of the spray-guided combustion systems. The results of research were presented in the form of index of variation of the selected parameters. The evaluation of the results of the optical research concerns radial spray penetration and fuel spray velocity. Unrepeatability has been presented with coefficient of variation of radial penetration in relation to the time of injection duration. It has been observed that the coefficients of various parameters are lower with longer times of fuel injection.
Highlights
Combustion systems of SI engines with direct injection at the time of mixture ignition require very precise synchronization of time of fuel spray penetration in the direction of the spark plug
The studies presented below were designed to obtain answers to the question of uniformity of the fuel spray penetration during high-pressure injection of fuel from the system of outward-opening type. This uniformity was determined on the basis of: a) the radial penetration of the fuel spray P obtained for the injector; these tests were carried out for the round angle of fuel spray atomization with resolution of 2 degrees; as a criterion for the maximum permissible value of nonuniformity was assumed the 5% coefficient of variation of the radial penetration in relation to the circular profile of such a flow
The presented analysis of the non-uniformity of fuel spray penetration and non-uniformity of its velocity makes it possible to draw several conclusions: 1. The fuel injection from injectors of outward-opening type is characterized by a high repeatability of the radial spray penetration for the time range from t = 0.1 to 0.5 ms during injection of small doses, and for the time range from t = 0.1 to 0.2 ms for large doses of fuel injected
Summary
Combustion systems of SI (spark ignition) engines with direct injection at the time of mixture ignition require very precise synchronization of time of fuel spray penetration in the direction of the spark plug. The studies presented below were designed to obtain answers to the question of uniformity of the fuel spray penetration during high-pressure injection of fuel from the system of outward-opening type. This uniformity was determined on the basis of: a) the radial penetration of the fuel spray P obtained for the injector; these tests were carried out for the round angle of fuel spray atomization with resolution of 2 degrees; as a criterion for the maximum permissible value of nonuniformity was assumed the 5% coefficient of variation of the radial penetration in relation to the circular profile of such a flow. The characteristics of the electrical signal (5V, TTL) for controlling the forced start of fuel injection, the time of its duration as well as the start time of images recording was provided by the sequencer with time resolution of 2 ns [12]
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