Abstract
Abstract
The compression stroke is an important index for engine operation because in-cylinder conditions at the end of compression have a major effect on its overall performance and efficiency. It is widely recognized that the compression stroke is strongly affected, beyond heat losses, by the initial pressure at inlet valve closure, the compression ratio (CR), and the blow-by rate. However, when a compression degradation is detected (i.e. decrease in peak compression pressure), it is very difficult to directly define the actual cause for this. In the present work, an advanced diagnostic technique is used to estimate the compression condition of a direct injection diesel engine and determine the actual cause for a reduction in peak compression pressure. To validate the proposed technique, a detailed experimental investigation was conducted on a single-cylinder test engine installed in the author's laboratory. At first, measurements were taken during the engine's normal operation (i.e. firing and motoring conditions). Then, ‘virtual’ faults have been created on the engine (i.e. reduced CR, cylinder mass leakage increase, and inlet chocking), aiming to reduce the peak compression pressure. The diagnostic technique is applied for each test case to estimate the cylinder compression condition and to detect the actual parameter that causes a decrease in peak compression pressure. The diagnosis results reveal that the technique can determine correctly the actual parameter responsible for compression deterioration in each case. This is accomplished even in cases where a combination of faults exists. The results obtained are extremely valuable, because the proposed diagnostic technique can be applied to any type of diesel engine and mainly to large-scale diesel engines (i.e. marine or stationary applications), where the application of non-catastrophic methods (i.e. without modifications or interventions to the engine cylinder) for estimating the cylinder compression conditions is extremely important.
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