Towards model-based control of RCCI-CDF mode-switching in dual fuel engines

The operation of a dual fuel combustion engine using combustion mode-switching offers the benefit of higher thermal efficiency compared to single-mode operation. For various fuel combinations, the engine research community has shown that running dual fuel engines in Reactivity Controlled Compression Ignition (RCCI) mode, is a feasible way to further improve thermal efficiency compared to Conventional Dual Fuel (CDF) operation of the same engine. In RCCI combustion, also ultra-low engine-out NOx and soot emissions have been reported. Depending on available hardware, however, stable RCCI combustion is limited to a certain load range and operating conditions. Therefore, mode-switching is a promising way to implement RCCI in practice on short term. In this paper, a model-based development approach for a dual fuel mode-switching controller is presented. Simulation results demonstrate the potential of this controller for a heavy-duty engine running on natural gas and diesel. An existing control-oriented engine model is extended with a new CDF model to simulate both CDF and RCCI operation. This model shows good agreement with experimental data. As a first step towards model-based control development, this extended model is used for system analysis to understand the switching behavior and to design a coordinated air-fuel path controller. This closed-loop controller combines static decoupling with next-cycle CA50-IMEP-Blend Ratio control. For a mode-switching sequence in a low load operating point, the closed-loop controlled engine demonstrates stable behavior and good reference tracking. The paper concludes with an outlook on necessary steps to bring model-based control strategies for dual fuel mode-switching in a multi-cylinder engine on the road

Coordinated air-fuel path control in a diesel-E85 RCCI engine

Reactivity Controlled Compression Ignition (RCCI) combines very high thermal efficiencies with ultra-low engine out NOx and PM emissions. Moreover, it enables the use of a wide range of fuels. As this pre-mixed combustion concept relies on controlled auto-ignition, closed-loop combustion control is essential to guarantee safe and stable operation under varying operating conditions. This work presents a coordinated air-fuel path controller for RCCI operation in a multi-cylinder heavy-duty engine. This is an essential step towards real-world application. Up to now, transient RCCI studies focused on individual cylinder control of the fuel path only. A systematic, model-based approach is followed to design a multivariable RCCI controller. Using the Frequency Response Function (FRF) method, linear models are identified for the air path and for the combustion process in the individual cylinders. From timing and blend ratio (BR) sweeps, it is decided to realize the high-level control objectives by controlling CA50, IMEP, BR and λ. Based on the identified models, a static decoupling is designed for the combined air-fuel system. For the decoupled system, a PI air path controller and three next cycle PI fuel path controllers are designed. The potential of the proposed control strategy is demonstrated on a six cylinder test set-up, which is equipped with the standard direct injection system for diesel and with an added port fuel injection system for E85. For engine speed and load steps, the RCCI controller is shown to have good tracking performance during transients. Compared to the open-loop control case, this controller is found to enhance combustion stability and to reduce THC and CO emissions

Towards model-based control of RCCI-CDF mode-switching in dual fuel engines

The operation of a dual fuel combustion engine using combustion mode-switching offers the benefit of higher thermal efficiency compared to single-mode operation. For various fuel combinations, the engine research community has shown that running dual fuel engines in Reactivity Controlled Compression Ignition (RCCI) mode, is a feasible way to further improve thermal efficiency compared to Conventional Dual Fuel (CDF) operation of the same engine. In RCCI combustion, also ultra-low engine-out NOx and soot emissions have been reported. Depending on available hardware, however, stable RCCI combustion is limited to a certain load range and operating conditions. Therefore, mode-switching is a promising way to implement RCCI in practice on short term.\u3cbr/\u3e\u3cbr/\u3eIn this paper, a model-based development approach for a dual fuel mode-switching controller is presented. Simulation results demonstrate the potential of this controller for a heavy-duty engine running on natural gas and diesel. An existing control-oriented engine model is extended with a new CDF model to simulate both CDF and RCCI operation. This model shows good agreement with experimental data. As a first step towards model-based control development, this extended model is used for system analysis to understand the switching behavior and to design a coordinated air-fuel path controller. This closed-loop controller combines static decoupling with next-cycle CA50-IMEP-Blend Ratio control. For a mode-switching sequence in a low load operating point, the closed-loop controlled engine demonstrates stable behavior and good reference tracking. The paper concludes with an outlook on necessary steps to bring model-based control strategies for dual fuel mode-switching in a multi-cylinder engine on the road.\u3cbr/\u3

Coordinated air-fuel path control in a diesel-E85 RCCI engine

Reactivity Controlled Compression Ignition (RCCI) combines very high thermal efficiencies with ultra-low engine out NOx and PM emissions. Moreover, it enables the use of a wide range of fuels. As this pre-mixed combustion concept relies on controlled auto-ignition, closed-loop combustion control is essential to guarantee safe and stable operation under varying operating conditions.\u3cbr/\u3e\u3cbr/\u3eThis work presents a coordinated air-fuel path controller for RCCI operation in a multi-cylinder heavy-duty engine. This is an essential step towards real-world application. Up to now, transient RCCI studies focused on individual cylinder control of the fuel path only. A systematic, model-based approach is followed to design a multivariable RCCI controller. Using the Frequency Response Function (FRF) method, linear models are identified for the air path and for the combustion process in the individual cylinders. From timing and blend ratio (BR) sweeps, it is decided to realize the high-level control objectives by controlling CA50, IMEP, BR and λ. Based on the identified models, a static decoupling is designed for the combined air-fuel system. For the decoupled system, a PI air path controller and\u3cbr/\u3ethree next cycle PI fuel path controllers are designed. The potential of the proposed control strategy is demonstrated on a six cylinder test set-up, which is equipped with the standard direct injection system for diesel and with an\u3cbr/\u3eadded port fuel injection system for E85. For engine speed and load steps, the RCCI controller is shown to have good tracking performance during transients. Compared to the open-loop control case, this controller is found to enhance\u3cbr/\u3ecombustion stability and to reduce THC and CO emissions

A closer look into a T-Tree test-node.

<p>The group 1 is tested. Out of this group, three SNPs are exploited by the weak learner. In red (resp. green), probability of being a case (resp. control) estimated by the weak-learner.</p