Engine knock margin control using in-cylinder pressure data: preliminary results

Knock is an undesired phenomenon occurring in spark ignited engines and is controlled acting on the spark timing. This paper presents a closed-loop architecture that makes possible to address the knock control problem with a standard model-based design approach. An engine knock margin estimate is feedback controlled through a PI regulator and its target value is computed starting from the desired knock probability. A black-box modelling approach is used to identify the dynamics between the spark timing and the knock margin and a traditional model-based controller synthesis is performed. Experimental results at the test bench show that, compared to a conventional strategy, the proposed approach allows for a better compromise between the controller speed and the variability of the spark timing. Moreover, another advantage w.r.t. the conventional strategies is that closed-loop performance prove to be constant for different reference probabilities, leading to a more regular engine behaviour

가솔린 엔진에서의 0-D 노킹 발생예측 모델링에 관한 연구

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2019. 2. 민경덕.가솔린 엔진의 효율 향상은 지속적으로 연구되어 왔으나, 최근의 급격히 강화되는 연비, 배기 규제로 인해 효율 향상의 필요성이 그 어느 때보다 더욱 대두되고 있다. 따라서 가솔린 엔진의 효율 향상을 위한 다양한 방법이 제시되고 있으며, 그 중에서도 압축비의 상승은 효율 개선에 매우 효과적이다. 그러나 압축비의 상승은 혼합기의 초기 온도를 상승시키며, 이는 연소기간 중 말단가스의 온도 상승으로 직결되어 미연 가스의 자발화 현상이 발생하기 쉽게 한다. 자발화 현상이 폭발의 형태로 발생하는 경우, 순간적인 열 방출이 발생하고 실린더 내부에 압력파를 형성하여 소음과 엔진 손상을 유발한다. 이는 노킹 현상으로 불리며, 엔진 손상을 방지하기 위하여 반드시 회피되어야 한다. 따라서 이에 대해 노킹을 저감하는 연구뿐만 아니라, 노킹을 회피하기 위한 다양한 제어 알고리즘이 제시되고 있다. 기존 양산 차량에서의 노킹 제어 알고리즘은 노킹 센서에 의존하고 있으며, 이는 센서에서 노킹 발생을 감지하는 것이 선행되어야 하므로 노킹을 완전히 회피할 수 없다. 또한, 노킹 발생 시 회피를 위해 제어인자가 급격히 변경되며, 이는 운전편의성이 나빠질 뿐만 아니라, 엔진 효율을 감소시키게 된다. 이러한 점을 개선하기 위해 제어인자를 점진적으로 변경하는 등 진보적인 제어 방법이 개발되고 있다. 노킹현상은 엔진 내의 유동, 열 전달 및 연소 특성과 같은 인자에 영향을 받으므로, 무작위적인 특성을 보인다. 따라서, 노킹을 보수적으로 회피하기 위해 기존의 제어는 노킹 회피 후에 운전 인자를 천천히 최적 운전 조건으로 복귀시킨다. 이는 전반적으로 효율이 낮은 지점에 운전 조건을 유지시키므로, 이를 개선한다면 고부하 조건에서 추가적인 효율 상승을 기대할 수 있다. 이에 대한 개선 방법의 하나로 노킹을 예측하여 선재적으로 제어를 수행하는 모델 기반의 제어를 제시할 수 있다. 이 경우, 노킹을 회피하기 용이해 질 뿐만 아니라, 노킹 발생 사전에 제어 인자를 지정함으로써 기존에 발생하던 과도한 제어 인자 변경으로 인한 효율 저하를 방지할 수 있다. 본 연구에서는 선재적 제어를 위한 기저연구로, 엔진에서의 노킹 발생 예측에 대한 모델링이 이루어졌다. 모델에는 실제 운전 상황에의 적용을 고려하여, 기존 양산 엔진에서 얻을 수 있는 변수 및 측정값만이 이용되었다. 첫째로, 실린더 내 압력 예측 모델링이 이루어 졌으며, 이는 실린더 내부 초기 조건의 판정, 압축기간 동안의 압력 예측, 그리고 연소율을 이용한 연소 압력 예측의 세가지 과정으로 진행되었다. 둘째로, 예측된 압력을 이용하여 미연가스의 온도를 계산하였으며, 이는 점화 지연을 계산하는 데에 이용되었다. 점화 지연은 실제 자발화 발생 여부를 판정하지 못하므로, 예측된 자발화 시점에서의 연소율을 이용하여 노킹 여부를 판정하였다. 구성된 모델은 사이클 별 편차가 고려된 압력 예측모델과 함께 적용되었을 경우 노킹 발생 빈도를 잘 예측하여, 충분한 예측 정확성을 가지고 있다고 판단되었다.Though the efficiency improvements of gasoline engines have been continually studied, the recent surge in fuel efficiency and emissions regulations has made the need for greater effort on efficiency improvement than ever before. Therefore, various methods have been proposed to improve the efficiency of gasoline engines, and among them, the increase in compression ratio has been known to be effective in improving fuel efficiency. However, the higher compression ratio increases the initial temperature of the mixture, which is led to in-cylinder condition which auto-ignition is likely to occur. If auto-ignition occurs in the form of an explosion, a stiff heat release occurs and forms a pressure wave inside the cylinder, causing noise and engine damage. This is called a knock and must be avoided to prevent engine damage. Therefore, various control algorithms have been proposed to avoid knock as well as researches to mitigate knock. Knocking control algorithms in conventional mass-produced vehicles rely on knock sensors. Because it is preceded by detection of knock from sensors, knock cannot be completely avoided. In addition, the control parameters change rapidly to avoid convolutions in case of knock, which not only deteriorates the driving convenience but also decreases fuel efficiency In order to improve this point, progressive control methods are being developed. The knock phenomenon is influenced by factors such as gas flow, heat transfer and combustion characteristics in the engine, so that it shows random characteristics. Therefore, in order to avoid the knocking conservatively, the conventional control slowly returns the operating parameters to the optimum condition after knocking avoidance. This maintains the operating conditions at lower efficiency points, so additional efficiency improvement is expected in high load condition if the control algorithm is improved. As one of the solutions, an advanced control with knock prediction can be suggested. In this case, not only is it able to avoid knock, but also by determining control factors prior to knock occurrence, it is also possible to avoid efficiency deterioration due to excessive change in control parameters. In this study, modeling of knock prediction was done as a base study for model based control. In the model, only operating parameters and measured values obtainable from the mass production engine were used, considering the application to actual driving conditions. Firstly, the in-cylinder pressure prediction modeling was done with three stepsdetermination of the initial conditions inside the cylinder, pressure prediction during the compression, and combustion pressure prediction using the burn rate. Additionally, with consideration on variation of Wiebe function, the cyclic variation model was constructed. Secondly, the temperature of the unburned gas was calculated using the predicted pressure. With those value, the ignition delay was calculated. Since the ignition delay only determines the onset of auto-ignition, not the occurrence, the burn rate at predicted onset was used to determine the knock occurrence. The pressure prediction and ignition delay model were combined to a single model and tested with cyclic variation model. As a result, the model was judged to have sufficient accuracy, predicting knock incidence accurately under various operating conditions.Abstract i Contents iv List of Tables vi List of Figures vii Nomenclature ix Chapter 1. Introduction 1 1.1 Backgrounds and Motivations 1 1.2 Literature Review 6 1.2.1 Auto-ignition and knock phenomenon 6 1.2.2 Knock methodologies 10 1.2.3 Knock mitigation strategies 16 1.3 Research objective 20 Chapter 2. Methodology 21 2.1 Test cell configuration 21 2.1.1 Test engine specification 21 2.1.2 Cell facility and equipment 21 2.2 Experimental conditions 26 2.2.1 Knock detection and incidence 26 2.2.2 Operating condition 26 2.3 Combustion analysis 29 2.3.1 Heat release rate and heat loss 29 2.3.2 Knock onset determination 33 2.3.3 Unburned gas temperature 36 2.3.4 Residual gas fraction estimation 37 Chapter 3. Model Description 44 3.1 Prediction of in-cylinder pressure 44 3.1.1 Initial gas state 44 3.1.2 Compression process with polytropic index model 46 3.1.3 Combustion process estimation 50 3.1.4 Simulation of cyclic variation 57 3.2 Criteria for knock determination 60 3.2.1 Ignition delay estimation 60 3.2.2 Mass burned fraction and knock onset 63 Chapter 4. Result and discussion 65 Chapter 5. Conclusion 70 Bibliography 73 국 문 초 록 82Maste

Development of Combustion Indicators for Control of Multi-Fuel Engines Based on New Combustion Concepts

[ES] Debido a las regulaciones en materia de emisiones y CO2 la industria automotriz a desarrollado diferentes tecnologías innovadoras. Estas tecnologías incluyen combustibles alternativos y nuevos modos de combustión, entre otros. De aquí surge la necesidad del desarrollo de nuevos métodos para el control de la combustión en estas condiciones mencionadas. Por este motivo, en este trabajo se han desarrollado diferentes modelos e indicadores orientados al diagnóstico y control de la combustión tanto en condiciones normales como anormales. Para los casos de combustión normal, se ha desarrollado un modelo de combustión, cuyo objetivo es estimar la media de la evolución de la fracción de la masa quemada y la presión dentro del cilindro. Se implementó un observador, basado en la señal de knock, con la finalidad de mejorar la estimación en condiciones transitorias y poder aplicar así el modelo a diferentes tipos de combustibles. También se presenta un modelo de variabilidad cíclica, en el cual, a partir del modelo de combustión, se propaga una distribución en dos de los parámetros de dicho modelo. Ambos modelos han sido aplicados para un motor de encendido provocado y un motor de combustión de encendido por chorro turbulento. En los casos de combustión anormal, se ha incluido un análisis de la resonancia dentro de la cámara de combustión, en donde también se desarrollaron dos modelos capaces de estimar la evolución de la resonancia. Estos modelos, tanto para condiciones normales como anormales, se utilizaron para el diagnóstico de la combustión. Por una parte, para la detección de knock, en donde tres estrategias de detección de knock fueron desarrolladas: dos basadas en el sensor de presión en cámara y una en el sensor de knock. Por otra parte, se realizó una aplicación de un modelo de resonancia para la mejora de la estimación de la masa atrapada a partir de la resonancia. Finalmente, para mostrar el potencial de los modelos de diagnóstico, dos aplicaciones a control se desarrollaron: una para el control de knock a través de la actuación de la chispa, y otra para el control de gases residuales, a través de la actuación de la distribución variable, realizando paralelamente una optimización de la combustión a través de la actuación de la chispa.[CA] Impulsada per les regulacions en matèria d'emissions i CO2 la indústria automotriu a desenvolupat diferents tecnologies inovadore. Aquestes tecnologies inclouen combustibles alternatius i nous modes de combustió, entre altres. D'ací sorgix la necessitat posar en pràctica nous mètodes per al control de la combustió. En aquest context, el present trevall proposa diferents models i indicadors orientats al diagnòstic i control de la combustió tant en condicions normals com anormals. Per als casos de combustió normal, es proposa un model de combustió, l'objectiu del qual és estimar la mitjana de l'evolució de la fracció de la massa cremada i la pressió dins del cilindre. Es va implementar un observador, basat en la senyal de knock, amb la finalitat de millorar l'estimació en condicions transitòries i poder aplicar així el model a diferents tipus de combustibles. També es presenta un model de variabilitat cíclica, en el qual, a partir del model de combustió, es propaga una distribució en dos dels parametres del dit model. Ambdós models han sigut aplicats a un motor d'encesa provocada i un motor de combustió d'encesa per doll turbulent. Als casos de combustió anormal, s'ha inclos un anàlisi de la ressonància dins de la cambra de combustió, on també es van desenvolupar dos models capaços d'estimar l'evolució de la ressonància. Aquests models, tant per a condicions normals com anormals, s'utilitzen per al diagnòstic de la combustió. Per una part, per a la detecció de knock, on tres estratègies de detecció de knock s'han desenvolupat: dues basades en el sensor de pressió a la cambra de combustió i una altra basada en el sensor de knock. Per altra part, es va realitzar una aplicació d'un model de ressonància per a la millora de l'estimació de la massa atrapada a partir de la ressonància. Finalment, per a mostrar el potencial dels models de diagnòstic, dos aplicacions de control es van desenvolupar: una per al control de knock a través de l'actuació de l'espurna, i una altra per al control de gasos residuals, a través de l'actuació de la distribució variable, realitzant paral·lelament una optimització de la combustió a través de l'actuació de l'espurna.[EN] The need to satisfy emissions and CO2 regulations is pushing the automotive industry to develop different innovative technologies. These technologies include alternative fuels and new modes of combustion, among others. Therefore, the need for the development of new methods for combustion control in these mentioned conditions arises. For this reason, in this work different models and indicators have been developed aimed at the diagnosis and control of combustion in both normal and abnormal conditions. For normal combustion cases, a combustion model has been developed, the objective of this model is to estimate the mean of evolution of the mass fraction burned and the in-cylinder pressure. An observer had been implemented, based on knock sensor signal, in order to improve the estimation in transient conditions and also to be able to make use of the model with different fuels. A cyclic variability model is also presented, where from the combustion model, a probability distribution is propagated over two of the parameters of such model. Both models had been applied for a spark ignition engine and a turbulent jet ignition combustion engine. For the abnormal combustion cases, an analysis of the resonance within the combustion chamber had been included, where two models capable of estimating the evolution of the resonance were also developed. These models, for both normal and abnormal conditions, were used for the diagnosis of combustion: on the one hand, for knock recognition, where three knock detection strategies were developed: two based on the in-cylinder pressure sensor and one on the knock sensor. On the other hand, an application of a resonance model was carried out in order to improve the estimation of the trapped mass from the resonance excitation. Finally, to show the potential of such models and applications, two control strategies were developed: one for the control of knock through the actuation of the spark advance, and a second for the control of residual gases, through the actuation of the variable valve timing, while optimizing the combustion through the actuation of the spark advance.El trabajo desarrollado en esta tesis ha sido posible gracias a la financiación de la Generalitat Valenciana y el fondo social europeo a través de la beca 132 GRISO- LIAP/2018/132 y BEFPI/2021/042.Jiménez, IA. (2022). Development of Combustion Indicators for Control of Multi-Fuel Engines Based on New Combustion Concepts [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/181561TESI

In-cylinder pressure resonance analysis for trapped mass estimation in automotive engines

This thesis presents a new application for in-cylinder pressure sensors in internal combustion engines. The new method takes profit of the high-frequency content of the in-cylinder pressure signal to determine the speed of sound evolution during the expansion stroke and combines this estimation with the low-frequency content of the pressure signal and a volume estimation to obtain a measurement of the trapped mass. The new method is based on the studies of the resonance phenomenon in pent-roof combustion chambers and proposes three calibration procedures to determine the resonant frequency evolution when bowl-in-piston geometries are considered. The Fourier transform has been modified in order to include harmonics with frequency variations, which allows a rapid identification of the resonant modes with no need of time-frequency analysis, e.g. STFT or WD. The main limitation of the method resides in the resonance excitation, which may be insufficient in low-load conditions, such as idle. An observer is presented to overcome that problem. The observer takes into account the dynamics of the sensors, the dynamics at the intake manifold, and combines current flow sensors with intermittent measurements, such as the trapped mass obtained by the resonance method, to provide the system with accurate and robust measurements of the trapped mass, the EGR, and the composition at the exhaust. The trapped mass obtained by the resonance method has been compared with auxiliary methods in various experimental facilities: in a SI engine, where no EGR exist, the differences founded were below 1%, in a conventional CI light-duty engine the average of the differences over 808 operating conditions accounted for a 2.64 %, in a research heavy-duty RCCI engine, with EGR, port fuel gasoline, and direct diesel injections, the average difference was 2.17 %, and in a research two-strokes single cylinder engine, where significant short-circuit and residual gases exist, the differences founded were 4.36 %. In all the studied cases the differences founded with the reference estimation can be attributed to the auxiliary method employed and its expected error. In order to demonstrate the potential of the resonance method four applications for control and diagnosis of internal combustion engines have been proposed: the estimation of residuals in engines with NVO, the prediction of knock in SI engines, the estimation of the exhaust gases temperature, and a NOx model for CI engines. In the four applications the method was compared with current methodologies and with additional sensors, demonstrating the improvement in accuracy and a cycle-to-cycle resolution.Esta tesis presenta una nueva aplicación para los sensores de presión en cámara. El nuevo método utiliza el contenido de alta frecuencia de la señal de presión en cámara para estimar la evolución de la velocidad del sonido durante la expansión de los gases de escape y combina esta estimación con el contenido de baja frecuencia de la presión en cámara y el volumen instantáneo de la cámara para obtener una medida de la masa atrapada. El nuevo método está basado en los estudios de la resonancia en cámaras de combustión cilíndricas y propone tres procedimientos de calibración para estimar la evolución de la frecuencia de resonancia en cámaras de combustión con bowl. La transformada de Fourier ha sido modificada para considerar harmónicos con frecuencias que varían en el tiempo, lo que permite una rápida identificación de los modos de resonancia sin necesidad de utilizar un análisis en tiempo frecuencia, como por ejemplo STFT o WD. La principal limitación del método es la necesidad de excitación suficiente de la resonancia, que puede impedir su uso en condiciones de baja carga como el ralentí. Para solventar este problema se ha diseñado un observador. El observador incluye las dinámicas de los sensores, las dinámicas del colector de admisión, y combina los sensores actuales de flujo con medidas intermitentes (como la medida ofrecida por el nuevo método de la resonancia) para obtener medidas de la masa atrapada, del EGR y de la composición en el escape precisas y robustas. La medida de la masa atrapada obtenida por el método de la resonancia ha sido comparado con métodos auxiliares en diferentes instalaciones experimentales: en un motor SI, sin EGR, las diferencias con los sensores eran menores del 1%, en un motor convencional CI la media de las diferencias sobre 808 puntos de operación distintos ha sido de 2.64 %, en un motor de investigación con EGR, con inyección gasolina en el colector e inyección directa de diesel, las diferencias fueron de 2.17 %, y en un motor de investigación de dos tiempos, donde existían grandes cantidades de corto-circuito y gases residuales, las diferencias fueron de 4.36 %. En todos los casos estudiados las diferencias encontradas pueden ser atribuidas a los errores que caracterizan los métodos auxiliares utilizados para obtener la medida de referencia. Finalmente, para demostrar el potencial del método se han desarrollado cuatro aplicaciones para control y diagnóstico de motores de combustión interna alternativos: la estimación de gases residuales en motores con NVO, la predicción de knock en motores SI, la estimación de la temperatura de los gases de escape, y un modelo de NOx para motores CI. En las cuatro aplicaciones el método ha sido comparado con los sistemas de medidas actuales y con sensores adicionales, demostrando mejoras importantes en la precisión de la medida y una resolución de un solo ciclo.Aquesta tesi presenta una nova aplicació per als sensors de pressió en cambra. El nou mètode utilitza el contingut d'alta freqüència del senyal de pressió en cambra per estimar l'evolució de la velocitat del so durant l'expansió dels gasos d'eixida i combina aquesta estimació amb el contingut de baixa freqüència de la pressió en cambra i el volum instantani de la cambra per obtenir una mesura de la massa atrapada. El nou mètode està desenvolupat dels estudis de la ressonància en cambres de combustió cilíndriques i proposa tres procediments de calibratge per estimar l'evolució de la freqüència de ressonància en cambres de combustió amb bowl. La transformada de Fourier ha sigut modificada per considerar harmònics amb freqüències que varien en el temps, el que permet una ràpida identificació dels modes de ressonància sense necessitat d'utilitzar una anàlisi en temps-freqüència, com per exemple la STFT o la WD. La principal limitació del mètode és la necessitat d'excitació suficient de la ressonància, que pot impedir el seu ús en condicions de baixa càrrega, com al ralentí. Per solucionar aquest problema s'ha desenvolupat un observador. L'observador inclou les dinàmiques dels sensors, les dinàmiques del col·lector d'admissió, i combina els sensors actuals de flux amb mesures intermitents (com l'obtinguda pel nou mètode de la ressonància) per obtenir mesures de la massa atrapada, del EGR i de la composició d'eixida precises i robustes. La mesura de la massa atrapada obtinguda pel mètode de la ressonància ha sigut comparada en mètodes auxiliars en diferents instal·lacions experimentals: a un motor SI, sense EGR, les diferencies amb els sensors estaven per davall de l'1 %, a un motor convencional CI la mitja de les diferències sobre 808 punts d'operació diferents ha sigut de 2.64 %, a un motor d'investigació, en EGR, en injecció gasolina en el col·lector i injecció directa de dièsel, les diferències van ser de 2.17 %, i a un motor d'investigació de dos temps, on existien grans quantitats de curtcircuit i residuals, les diferencies foren de 4.36 %. En tots els casos estudiats les diferències trobades poden ser atribuïdes als errors que caracteritzen els mètodes auxiliars utilitzats per obtenir la mesura de referència. Finalment, per demostrar el potencial del mètode s'han desenvolupat quatre aplicacions per al control i diagnòstic de motors de combustió interna alternatius: l'estimació de gasos residuals en motors amb NVO, la predicció de knock en motors SI, l'estimació de la temperatura dels gasos d'eixida, i un model de NOx per a motors CI. En les quatre aplicacions el mètode ha sigut comparat amb els sistemes de mesures actuals i amb sensors addicionals, demostrant millores importants en la precisió de la mesura i una resolució de solament un cicle.Bares Moreno, P. (2017). In-cylinder pressure resonance analysis for trapped mass estimation in automotive engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/9042

Experimental Validation of a Likelihood-Based Stochastic Knock Controller

New likelihood-based stochastic knock controllers have the potential to deliver a significantly improved regulatory response relative to conventional strategies, while also maintaining a rapid transient response, but evaluation studies to date have been performed only in simulation. In this paper, an experimental validation of the new strategy is presented. To demonstrate the robustness of the method, the algorithm is implemented on two different engine platforms, using two different knock intensity metrics, and evaluated under different operating conditions. One of these platforms is a five-cylinder variable compression ratio engine, enabling the controller to be tested under different compression ratios, as well as different speed and load conditions. The regulatory and transient performance of the likelihood-based controller is assessed in a back-to-back comparison with a conventional knock controller and it is shown that the new controller is able to operate closer to the knock limit with less variation in control action without increasing the risk of engine damage.Funding Agencies|Briar Hill Foundation; ExxonMobil</p

A fuzzy logic map-based knock control for spark ignition engines

[EN] Knock control represents one of the most critical aspects to reach optimal thermal efficiency in spark ignition engines, and its research is crucially important because it determines thermal efficiency, engine durability, and power density, as well as noise and emission performance. In this paper, a spark advance control based on a map learning technique is combined with a knock estimator to maximize the engine efficiency while keeping the knock probability below a desired limit. The proposed controller is experimentally validated on a production spark ignition gasoline engine test bench, and compared with a conventional spark advance controller in both, steady and transient conditions. From experimental results, a benefit in terms of thermal efficiency, control stability and engine security are achieved. The results show that the proposed method is capable of regulating the knock probability to a target percentage with low spark advance and thermal efficiency dispersion than the conventional controller.Irina A. Jimenez received a funding through the grant GRISOLIAP/2018/132 from the Generalitat Valenciana and the European Social Fund.Pla Moreno, B.; Bares-Moreno, P.; Jimenez, IA.; Guardiola, C.; Zhang, Y.; Shen, T. (2020). A fuzzy logic map-based knock control for spark ignition engines. Applied Energy. 280:1-8. https://doi.org/10.1016/j.apenergy.2020.116036S18280Liu, H., Wang, C., Yu, Y., Xu, H., & Ma, X. (2020). An experimental study on particle evolution in the exhaust gas of a direct injection SI engine. Applied Energy, 260, 114220. doi:10.1016/j.apenergy.2019.114220Chen, C., Pal, P., Ameen, M., Feng, D., & Wei, H. (2020). Large-eddy simulation study on cycle-to-cycle variation of knocking combustion in a spark-ignition engine. 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