Abstract
The paper presents the results of strength test simulations of the CNG injector structure for direct injection of compression-ignition engines. This article is a continuation of the works presented in paper [1]. Life cycles estimation of particular parts of the injector were calculated using the Kocańda relation. The simulation tests of injector strength carried out earlier have allowed us to determine the stress concentration points. On the basis of NEDC driving tests carried out in three different cars, engine load histograms were made for subsequent runs and an average load profile was determined. For the points most exposed to damage,i.e.the needle and injector housing, the stress curve was generated as a function of time. This dependence was the base for fatigue calculations with the use of MatLab program in order to calculate the limit number of repetitions for a given injector element. All the calculation works have served to determine the maximum number of work cycles of a given injector design.
Highlights
The use of simulation studies for design optimisation is commonplace
On the basis of these measurements, engine load histograms were created for subsequent journeys and average load profiles determined (3 vehicles, 3 journeys, urban and extra-urban)
The initial fatigue calculations proved that the needle body is the element of the injector most susceptible to damage
Summary
Mainly due to the lack of access to computers with high computing power, it was not possible to perform strength and fatigue analysis of complex structures. The formerly applied analytical methods were efficient but based on simple mathematical relationships that were suitable for static loads on the structure. Access to a wide range of simulation software (strength, fatigue, etc.) allows for substantial reductions in the designing time and optimisation of new structures [1, 2]. This applies mainly to machine elements operating under extreme loading conditions. Especially in recent times, there has been a multiplefold increase in the usability of this type of software [1]
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