Abstract
An innovative computationally efficient method for the simultaneous determination of top dead centre (TDC) offset and pressure offset is presented. It is based on characteristic deviations of the rate of heat release (ROHR) that are specific for both offsets in compression phase and expansion phase after the end of combustion. These characteristic deviations of the ROHR are derived from first principles and they were also confirmed through manual shifts of the pressure trace. The ROHR is calculated based on the first law of thermodynamics using an in-cylinder pressure trace, engine geometrical parameters and operating point specific parameters. The method can be applied in off-line analyses using an averaged pressure trace or in on-line analyses using a single pressure trace. In both application areas the method simultaneously determines the TDC position and the pressure offset within a single processing of the pressure trace, whereas a second refinement step can be performed for obtaining more accurate results as correction factors are determined more accurately using nearly converged input data. Innovative analytic basis of the method allows for significant reduction of the computational times compared to the existing methods for the simultaneous determination of TDC offset and pressure offset in fired conditions. The method was validated on a heavy-duty and a light-duty diesel engine.
Highlights
Reduction of exhaust emissions and simultaneous maintenance or even increasing of engine efficiency and specific power is a major challenge for engine manufacturers
rate of heat release (ROHR) deviations will be analysed for different pressure and top dead centre (TDC) offsets to provide experimental evidence on the hypotheses that ROHR features different characteristic deviations in the compression phase and the expansion phase when subjected to the TDC and the pressure offset
It might be worth noting that the results were calculated by applying Equation (4), which is commonly used in ROHR analyses, and equations proposed in Sections 2.2 and 2.3 were not used to generate any of the results
Summary
Reduction of exhaust emissions and simultaneous maintenance or even increasing of engine efficiency and specific power is a major challenge for engine manufacturers. Real driving emission tests will apply to the vehicles in service [2]. To comply with these requirements, manufacturers are focusing on controlling combustion process with various strategies, which need to be sufficiently robust for vehicles in service featuring components that are subjected to wear and ageing. One of the very promising strategies to approach the optima with respect to exhaust emissions and engine efficiency is the closed-loop combustion control (CLCC) using in-cylinder pressure sensors. CLCC adapts injection strategies according to the actual in-cylinder pressure trace and parameters that are derived thereof while considering parameters from other engine sensors
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