Transient Load-Speed Control in Multi-Cylinder Recompression HCCI Engines

Strict proposed fuel economy and emissions standards for automotive internal combustion engines have motivated the study of advanced low-temperature combustion modes that promise higher combustion efficiencies with low engine-out emissions. This work presents modeling and control results for one such combustion mode -- recompression homogeneous charge compression ignition (HCCI) combustion. Regulating desired charge properties in recompression HCCI involves the retention of a large amount of the residual charge between engine cycles, thus introducing significant inter-cycle feedback in the system. This work considers a baseline controller from literature, and proposes two improved model-based control strategies. The controllers use exhaust valve timing and fuel injection timings to track combustion phasings during transitions in the HCCI region of the multi-cylinder engine load-speed operating map. Fast and stable control of these transitions is demonstrated, which maximizes the length of stay in the HCCI region, and hence the efficiency benefit of advanced combustion. The baseline controller, which is a feedback-feedforward controller adapted from literature, is tuned using a low-order, discrete-time, control-oriented model that describes the stable, high efficiency HCCI region. The first improved control strategy augments the baseline controller with a reference or fuel governor that modifies transient fuel mass commands during large load transitions, when the possibility of future actuator constraint violations exists. This approach is shown in experiments to improve the combustion phasing and load responses, as well as prevent engine misfires. Issues with high cyclic variability during late phasing and low load conditions, and their impact on transient performance, are discussed. These issues are physically explained through recompression heat release caused due to unburned and recycled fuel. The control-oriented model is augmented with recompression heat release to predict the onset of the oscillatory, high variability region. The second improved control strategy uses this physical understanding to improve combustion phasing tracking performance. Transitions tested on a multicylinder HCCI engine include load transitions at fixed engine speeds, engine speed ramps at fixed load, simultaneous load and speed transitions, and select FTP75 drive-cycle transitions with high load slew rates. This improved model-based control strategy is proposed as a solution for the HCCI transient control problem.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107072/1/sjade_1.pd

Experimental Analysis and Control of Recompression Homogeneous Charge Compression Ignition Combustion at the High Cyclic Variability Limit.

The automotive industry currently faces many challenges pertaining to strict emissions and fuel consumption constraints for a sustainable society. These regulations have motivated the investigation of low temperature combustion modes such as homogeneous charge compression ignition (HCCI) as a potential solution to meet these demands. HCCI combustion is characterized by high efficiency and low engine-out emissions. However, this advanced combustion mode is limited in the speed-load operating space due to high pressure rise rates for increased loads. Often higher loads are run at later combustion phasings to reduce pressure rise rates, however high cyclic variability (CV) can also be a limiting factor for late combustion phasings. This work presents advancements in the understanding of high variability dynamics in recompression HCCI as well as methods for control of CV and load transitions which typically encounter regions of high variability. Standard in-cylinder pressure based analysis methods are extended for use on high variability data. This includes a method of determining the trapped residual mass in real time. Determination of the residual mass is critical in recompression HCCI because of the combustion's sensitivity to the thermal energy contained within the residual charge. Trapping too much or little residuals can lead to ringing or misfires and CV, respectively. Various levels of CV are studied using large experimental data sets to ensure statistical relevance. The cycle resolved analysis of this data has allowed for the development of a predictive model of the variability associated with lean late phasing combustion. This model is used to develop control which can suppress cyclic variability at steady state. Knowledge about steady state control of CV and its oscillatory dynamics is further applied to the development of an adaptive controller. The adaptive controller uses a parameter estimation scheme in the feedforward component of a baseline midranging structure. The adaptive feedforward component enables the ability to correct for modeling errors and reduces parameterization effort. Experimental results demonstrate that the control is effective at navigating through large load transients while avoiding excess amounts of variability. Additionally, the actuators spend more time in a region of high authority when compared to non-adaptive control.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107231/1/larimore_1.pd

Reactivity controlled compression ignition engine: Pathways towards commercial viability

© 2020 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (http://creativecommons.org/licenses/by-nc-nd/4.0/).Reactivity-controlled compression ignition (RCCI) is a promising energy conversion strategy to increase fuel efficiency and reduce nitrogen oxide (NOx) and soot emissions through improved in-cylinder combustion process. Considering the significant amount of conducted research and development on RCCI concept, the majority of the work has been performed under steady-state conditions. However, most thermal propulsion systems in transportation applications require operation under transient conditions. In the RCCI concept, it is crucial to investigate transient behavior over entire load conditions in order to minimize the engine-out emissions and meet new real driving emissions (RDE) legislation. This would help further close the gap between steady-state and transient operation in order to implement the RCCI concept into mass production. This work provides a comprehensive review of the performance and emissions analyses of the RCCI engines with the consideration of transient effects and vehicular applications. For this purpose, various simulation and experimental studies have been reviewed implementing different control strategies like control-oriented models particularly in dual-mode operating conditions. In addition, the application of the RCCI strategy in hybrid electric vehicle platforms using renewable fuels is also discussed. The discussion of the present review paper provides important insights for future research on the RCCI concept as a commercially viable energy conversion strategy for automotive applications.Peer reviewe

EXPERIMENTAL SETUP AND CONTROLLER DESIGN FOR AN HCCI ENGINE

Homogeneous charged compression ignition (HCCI) is a promising combustion mode for internal combustion (IC) engines. HCCI engines have very low NOx and soot emission and low fuel consumption compared to traditional engines. The aim of this thesis is divided into two main parts: (1) engine instrumentation with a step towards converting a gasoline turbocharged direct injection (GTDI) engine to an HCCI engine; and (2) developing controller for adjusting the crank angle at 50% mass fuel burn (CA50), exhaust gas temperature Texh, and indicated mean effective pressure (IMEP) of a single cylinder Ricardo HCCI engine. The base GTDI engine is modified by adding an air heater, inter-cooler, and exhaust gas recirculation (EGR) in the intake and exhaust loops. dSPACE control units are programmed for adding monitoring sensors and implementing actuators in the engine. Control logics for actuating electronic throttle control (ETC) valve, EGR valve, and port fuel injector (PFI) are developed using the rapid control prototyping (RCP) feature of dSPACE. A control logic for crank/cam synchronization to determine engine crank angle with respect to firing top dead center (TDC) is implemented and validated using in-cylinder pressure sensor data. A control oriented model (COM) is developed for estimating engine parameters including CA50, Texh, and IMEP for a single cylinder Ricardo engine. The COM is validated using experimental data for steady state and transient engine operating conditions. A novel three-input three-output controller is developed and tested on a detailed physical HCCI engine plant model. Two type of controller design approaches are used for designing HCCI controllers: (1) empirical, and (2) model-based. A discrete sub-optimal sliding mode controller (DSSMC) is designed as a model-based controller to control CA50 and Texh, and a PI controller is designed to control IMEP. The results show that the designed controllers can successfully track the reference trajectories and can reject the external disturbances within the given operating region

Modeling and Control of Maximum Pressure Rise Rate in RCCI Engines

Low Temperature Combustion (LTC) is a combustion strategy that burns fuel at lower temperatures and leaner mixtures in order to achieve high efficiency and near zero NOx emissions. Since the combustion happens at lower temperatures it inhibits the formation of NOx and soot emissions. One such strategy is Reactivity Controlled Compression Ignition (RCCI). One characteristic of RCCI combustion and LTC com- bustion in general is short burn durations which leads to high Pressure Rise Rates (PRR). This limits the operation of these engines to lower loads as at high loads, the Maximum Pressure Rise Rate (MPRR) hinders the use of this combustion strategy. This thesis focuses on the development of a model based controller that can control the Crank Angle for 50% mass fraction burn (CA50) and Indicated Mean Effective Pressure (IMEP) of an RCCI engine while limiting the MPRR to a pre determined limit. A Control Oriented Model (COM) is developed to predict the MPRR in an RCCI engine. This COM is then validated against experimental data. A statistical analysis of the experimental data is conducted to understand the accuracy of the COM. The results show that the COM is able to predict the MPRR with reasonable accuracy in steady state and transient conditions. Also, the COM is able to capture the trends during transient operation. This COM is then included in an existing cycle by cycle dynamic RCCI engine model and used to develop a Linear Parameter Varying (LPV) representation of an RCCI engine using Data Driven Modeling (DDM) approach with Support Vector Machines (SVM). This LPV representation is then used along with a Model Predictive Controller (MPC) to control the CA50 and IMEP of the RCCI engine model while limiting the MPRR. The controller was able to track the desired CA50 and IMEP with a mean error of 0.9 CAD and 4.7 KPa respectively while maintaining the MPRR below 5.8 bar/CAD

MODELING AND ANALYSIS OF REACTIVITY CONTROLLED COMPRESSION IGNITION (RCCI) COMBUSTION

Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) combustion strategies are promising methods for achieving low engine-out NOx and soot emissions as well as high indicated efficiency. However, these combustion strategies have difficulties with controlling the rate of heat release and lack of an adequate combustion phasing control mechanism. A dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion strategy will address these issues due to the existence of precise means for controlling the heat release rate and combustion phasing. In the RCCI strategy two fuels with different reactivity (auto-ignition characteristics, e.g., gasoline and diesel) are blended inside the combustion chamber. Combustion phasing is controlled by the relative ratios of these two fuels and the combustion duration is controlled by the local equivalence ratio gradient between the two fuels. This thesis focuses on development of RCCI engine combustion model and understanding the effects of key parameters controlling RCCI engine combustion. This thesis includes three major modeling and analysis contributions. In the first part, a computationally efficient modeling platform is developed and validated against the experimental data. The model is able to predict start of combustion (SOC) with average error around 1 Crank Angle Degree (CAD). However, due to premixed nature of air-fuel mixture and considering the whole combustion chamber as one uniform zone, the model over predicts peak in-cylinder pressure and therefore is not capable of predicting crank angle for 50 percent mass of fuel burned (CA50) and Burn Duration (BD). Proper operation of RCCI engines requires an in-depth understanding of the interactions between fluid flows, turbulent mixing and chemical kinetics. In the second part of this thesis, a detailed 3D/Computational Fluid Dynamics (CFD) combustion model in commercial CFD code called CONVERGE is developed and validated against experimental data. In-cylinder pressure trace, combustion phasing and emissions (e.g., NOx, HC and CO) are shown to be in good agreement with experimental data for different operating conditions. In the last part, the effects of fuel injection system parameters on the performance and emissions characteristics of an RCCI engine are discussed. The injection system parameters include Premixed Ratio (PR), injection pressure, Start of Injection (SOI) timing and spray angle. The CFD model is then used to suggest an injection strategy capable of achieving optimized RCCI engine operation

Modeling and experimental analysis of exhaust gas temperature and misfire in a converted-diesel homogeneous charge compression ignittion engine fuelled with ethanol

Homogeneous charge compression ignition (HCCI) and the exploitation of ethanol as an alternative fuel is one way to explore new frontiers of internal combustion engines with an objective towards maintaining its sustainability. Here, a 0.3 liter singlecylinder direct-injection diesel engine was converted to operate on the alternative mode with the inclusion of ethanol fuelling and intake air preheating systems. The main HCCI engines parameters such as indicated mean effective pressure, maximum in-cylinder pressure, heat release, in-cylinder temperature and combustion parameters, start of combustion, 50% of mass fuel burnt (CA50) and burn duration were acquired for 100 operating conditions. They were used to study the effect of varying input parameters such as equivalence ratio and intake air temperature on exhaust gas emission, temperature and ethanol combustion, experimentally and numerically. The study primarily focused on HCCI exhaust gas temperature and understanding and detecting misfire in an ethanol fuelled HCCI engine, thus highlighting the advantages and drawbacks of using ethanol fuelled HCCI. The analysis of experimental data was used to understand how misfire affects HCCI engine operation. A model-based misfire detection technique was developed for HCCI engines and the validity of the obtained model was then verified with experimental data for a wide range of misfire and normal operating conditions. The misfire detection is computationally efficient and it can be readily used to detect misfire in HCCI engine. The results of the misfire detection model are very promising from the viewpoints of further controlling and improving combustion in HCCI engines

Safe operation of dual-fuel engines using constrained stochastic control

This is the author¿s version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087420985109[EN] Premixed combustion strategies have the potential to achieve high thermal efficiency and to lower the engine-out emissions such as NOx. However, the combustion is initiated at several kernels which create high pressure gradients inside the cylinder. Similarly to knock in spark ignition engines, these gradients might be responsible of important pressure oscillations with a harmful potential for the engine. This work aims to analyze the in-cylinder pressure oscillations in a dual-fuel combustion engine and to determine the feedback variables, control actuators, and control approach for a safe engine operation. Three combustion modes were examined: fully, highly, and partially premixed, and three indexes were analyzed to characterize the safe operation of the engine: the maximum pressure rise rate, the ringing intensity, and the maximum amplitude of pressure oscillations (MAPO). Results show that operation constraints exclusively based on indicators such as the pressure rise rate are not sufficient for a proper limitation of the in-cylinder pressure oscillations. This paper explores the use of a knock-like controller for maintaining the resonance index magnitude under a predefined limit where the gasoline fraction and the main injection timing were selected as control variables. The proposed strategy shows the ability to maintain the percentage of cycles exceeding the specified limit at a desired threshold at each combustion mode in all the cylinders.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was financially support by the Programa Operativo del Fondo Social Europeo (FSE) de la Comunitat Valenciana 2014-2020 through grant ACIF/2018/141.Guardiola, C.; Pla Moreno, B.; Bares-Moreno, P.; Barbier, ARS. (2022). Safe operation of dual-fuel engines using constrained stochastic control. International Journal of Engine Research. 23(2):285-299. https://doi.org/10.1177/146808742098510928529923

Experimental and Computational Investigation of Spark Assisted Compression Ignition Combustion Under Boosted, Ultra EGR-Dilute Conditions

Low temperature combustion (LTC) engines that employ high levels of dilution have received increased research interest due to the demonstrated thermal efficiency improvements compared to the conventional Spark-Ignited (SI) engines. However, control of combustion phasing and heat release rate still remains a challenge, which limits the operating range as well as the transient operation of LTC engines. The work presented in this dissertation uses experimental and computational methods to investigate Spark Assisted Compression Ignition (SACI) combustion under boosted, stoichiometric conditions with high levels of exhaust gas recirculation in a negative valve overlap engine. Highly controlled experimental studies were performed to understand the impact of intake boosting and fuel-to-charge equivalence ratio (φ') on SACI burn rates, while maintaining constant combustion phasing near the optimal timing for work extraction. Previously unexplored conditions were targeted at intake pressures ranging from 80 kPa to 150 kPa and φ' ranging from 0.45 to 0.75, where LTC engines promise high thermodynamic efficiencies. The use of intake boosting for load expansion and dilution extension achieved up to 10% gross thermal efficiency improvement, respectively, mainly due to reduced relative heat transfer losses and better mixture thermodynamic properties. For a given spark advance, higher pressure and/or higher φ' mixtures necessitated lower unburned gas temperatures (TU) to match autoignition timing. While the overall effect of intake boost was minor on the initial flame burn rates, end-gas autoignition rates were found to approximately scale with intake pressure. Higher φ' mixtures exhibited faster initial flame burn rates but also led to a significant increase in end-gas autoignition rates. As a result, the high load limits shifted to lower φ' at higher intake pressures, creating a larger gap between the SI and SACI operating limits. Reducing the mass fraction unburned at the onset of autoignition by advancing the spark timing and lowering TU was, to some extent, effective at alleviating the excessive peak pressure rise rates. Under relatively high φ' conditions, cyclic heat release analysis results showed that the variability in autoignition timing is determined early in the cycle before any measurable pressure-based heat release. Combustion phasing retard was shown to be very effective at limiting the maximum pressure rise rates until the stability limit, primarily due to slower end-gas autoignition rates. CFD modeling results showed good trendwise agreement with the experimental results, once autoignition timing and mass fraction burned at the onset of autoignition were matched. The pre-ignition reactivity stratification of the mixture at higher intake pressures was shown to be narrower, due to both lower thermal and compositional stratification, which explained the increase in end-gas burn rates observed experimentally. The boost pressure effect on SACI end-gas burn rates using intake manifold heating was trendwise similar to the results employing residual gas heating, albeit less pronounced. Pre-ignition thermal stratification was shown to be similar irrespective of charge preheating method, even though thermal stratification of the mixtures was very different early in the compression stroke. The effect of higher pressure on mean reactivity was offset by the lower mean temperature that was needed to match autoignition timing. Under the conditions investigated, the increase in the end-gas autoignition rates with intake boost was primarily due to the narrower thermal stratification, which was effected by reduced relative heat transfer losses late in the compression stroke.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147508/1/vtrianto_1.pd