In-Zyklus Regelstrategien für ottomotorische Selbstzündung

• In-cycle control strategies for gasoline controlled autoignition

Lehrheuer, Bastian; Pischinger, Stefan (Thesis advisor); Andert, Jakob Lukas (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The key research task of this work is the development and investigation of control strategies for gasoline controlled autoignition that act within a combustion cycle in order to directly influence the combustion phasing, maximum pressure gradient, and fuel conversion. In addition to rapid detection of the thermodynamic state in the cylinder and prediction of the imminent combustion characteristics, the investigations focus on identifying suitable control interventions by means of direct water injection and spark assistance. The main elements of the determination of the thermodynamic state in the cylinder are the online three-pressure analysis and gas exchange calculation. Key parameters such as residual gas fraction, temperature of the gas in the cylinder and heat release are determined at any time during a cycle. It has been shown that delayed autoignition only becomes apparent in the cylinder pressure signal immediately before or at the targeted start of combustion. For this reason, a control strategy was developed based on the rapid detection of late combustion via the pressure level or heat release shortly before top dead center. By injecting water directly into the combustion chamber, the combustion phasing can be shifted toward late and the maximum pressure gradient is significantly reduced. Combustion phasing, pressure gradient, and combustion duration behave approximately proportionally to the mass of water introduced, with the effect becoming more pronounced as the residual gas content decreases or the load increases: Δφ50% = 1.4 °CA/mgH2O at an indicated mean effective pressure of pmi = 4 bar and an internal residual gas fraction of xegr = 51 % compared to Δφ50% = 6 °CA/mgH2O at pmi = 4.8 bar and xegr = 40 %. In addition, the behavior during cyclic actuation of water injection every second, third, and fifth cycle was investigated. This showed that the influence on the combustion immediately following a water injection is about half as pronounced as with an injection every cycle. As early as the second cycle after an injection, there is no longer any discernible influence of the water. Finally, the findings on control strategies with direct water injection and controlled spark assistance were combined, implemented on a prototyping ECU and tested on a single-cylinder research engine. All strategies can improve the standard deviation of the indicated mean effectice pressure, the combustion phasing, and the maximum pressure gradient. The highest potential is shown by a strategy based on the residual fuel mass when closing the exhaust valves with early water injection at φEBH2O = 270 ° CA aTDC in combination with an adapted fuel mass flow.

Institutions

• Chair of Themordynamics of Mobile Energy Conversion [412310]