Supervisory control of complex propulsion subsystems

Modern gasoline and diesel combustion engines are equipped with several subsystems with the goal to reduce fuel consumption and pollutant exhaust emissions. Subsystem synergies could be harnessed using the supervisory control approach. Look-ahead information can be used to potentially optimise power-train control for real time implementation. This thesis delves upon modelling the exhaust emissions from a combustion engine and developing a combined equivalent objective metric to propose a supervisory controller that uses look-ahead information with the objective to reduce fuel consumed and exhaust emissions. In the first part of the thesis, the focus is on diesel engine application control for emissions and fuel consumption reduction.\ua0Model of exhaust emissions in a diesel engine obtained from a combination of nominal engine operation and deviations are evaluated for transient drive cycles.\ua0The look ahead information as a trajectory of vehicle speed and load over time is considered.\ua0The supervisory controller considers a discrete control action set over the first segment of the trip ahead.\ua0The cost to optimise is defined and pre-computed off-line for a discrete set of operating conditions.\ua0A full factorial optimisation carried out off-line is stored on board the vehicle and applied in real-time.\ua0In a first proposal, the subsystem control of the after-treatment system comprising the lean NOx trap and the selective reduction catalyst is considered.\ua0As a next iteration, the combustion engine is added to the control problem.\ua0Simulation comparison of the controllers with the baseline controller offers a 1 % total fuel equivalent cost improvement while offering the flexibility to tailor the controller for different cost objective. In the second part of the thesis, the focus is on cold-start emissions control for modern gasoline engines.\ua0Emissions occurring when the engine is started until the catalyst is sufficiently warm, contribute to a significant proportion of tailpipe pollutant emissions.\ua0Electrically heated catalyst (EHC) in the three way catalyst (TWC) is a promising technology to reduce cold-start emissions where the catalyst can be warmed up prior to engine start and continued after start.\ua0A simulation framework for the engine, TWC with EHC with focus on modeling the thermal and chemical interactions during cold-start was developed.\ua0An evaluation framework with a proposed equivalent emissions approach was developed considering the challenges associated with cold-start emission control.\ua0An equivalent emission optimal post-heating time for the EHC is proposed that adapts to information which is available in a real-time on-line implementation.\ua0The proposed controller falls short of just 1 % equivalent emissions compared to the optimal case

Diesel Engine

Diesel engines, also known as CI engines, possess a wide field of applications as energy converters because of their higher efficiency. However, diesel engines are a major source of NOX and particulate matter (PM) emissions. Because of its importance, five chapters in this book have been devoted to the formulation and control of these pollutants. The world is currently experiencing an oil crisis. Gaseous fuels like natural gas, pure hydrogen gas, biomass-based and coke-based syngas can be considered as alternative fuels for diesel engines. Their combustion and exhaust emissions characteristics are described in this book. Reliable early detection of malfunction and failure of any parts in diesel engines can save the engine from failing completely and save high repair cost. Tools are discussed in this book to detect common failure modes of diesel engine that can detect early signs of failure

Supporting the regeneration process of a diesel particulate filter with the addition of hydrogen and hydrogen/carbon monoxide mixtures: diesel engine aftertreatment system

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel UniversityThis investigation aims to enhance the regeneration performance of a diesel particulate filter. This is achieved by introducing various chemical components to the regeneration process, which are representative of what can be generated ‘on board’ a vehicle using an exhaust gas fuel reformer. By researching the effects of introducing such components using a periodic injection cycle the aim is to reduce the volume of ‘reformates’ required to assist in proficient diesel particulate filter regeneration. As a result, this study also aims to support future work in the development of exhaust gas fuel reformer design for DPF aftertreatment applications. All experiments were performed using a Ford Puma 2.0 litre diesel engine. A test rig was constructed and installed that featured a mini diesel particulate filter housed within a tubular furnace. Exhaust gas could be sampled directly from the exhaust manifold and fed through the DPF. Exhaust gas measurements were taken both pre and post DPF using a FTIR spectrometer. It was shown that the regeneration process could be supported substantially by the introduction of hydrogen. Similar properties were also demonstrated when introducing a hydrogen-carbon monoxide mixture. The introduction of these species allowed for the regeneration process to be implemented at filter temperatures substantially lower than the passive regeneration temperature. Furthermore, by introducing these simulated reformates using a periodic injection strategy, it was evident that similar benefits to the regeneration process could be attained with significantly less volumes of simulated reformates. In an attempt to effectively utilise the carbon monoxide generated during hydrogen production by an exhaust gas fuel reformer, this study defined an optimised hydrogen/carbon monoxide mixture ratio of 60% (v/v) hydrogen balanced with carbon monoxide. At this optimised mixture ratio, the filter demonstrated the highest regeneration efficiency of all ratios tested. Such data could be utilised in future work in the development of fuel reformer design.Engineering and Physical Science Research Council (Grants EP/F025416/1 and EP/G038007/1)

Automotive Powertrain Control — A Survey

This paper surveys recent and historical publications on automotive powertrain control. Control-oriented models of gasoline and diesel engines and their aftertreatment systems are reviewed, and challenging control problems for conventional engines, hybrid vehicles and fuel cell powertrains are discussed. Fundamentals are revisited and advancements are highlighted. A comprehensive list of references is provided.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72023/1/j.1934-6093.2006.tb00275.x.pd

A Two Dimensional Numerical Soot Model for Advanced Design and Control of Diesel Particulate Filters

One of the most effective methods to control diesel particulate matter (PM) emissions from heavy duty diesel engines is to use wall flow diesel particulate filters (DPF). It is still a major challenge to get an accurate estimation of soot loading, which is crucial for the engine afterteratment assembly optimization. In the recent past, several advanced computational models of DPF filtration and regeneration have been presented to assess the cost effective optimization of future particulate trap systems. They are characterized by different degree of detail and computational costs, depending on the specific application (i.e diagnostics, control, system design, component design etc).;The objective of this study is to compare in detail a two dimensional (2-D) approach with a one dimensional (1-D) approach, thus giving a better insight of the variation of properties over the DPF length. This task has been archived by extending an in-house developed 1-D numerical soot model to the next dimension to understand the impact of 2-D representation to predict both steady state and transient behavior of a catalyzed diesel particulate filter (CDPF). Performance of the model was evaluated using three key parameters: pressure drop, filter outlet temperature and soot mass retained in the filter during both active and continuous regeneration events. Quasi-steady state conservation of mass, momentum and energy equations were solved numerically using finite difference methods adopting a spatially uniform mesh. The results obtained from the current model were compared with the 1-D code to evaluate the general validity of assumptions made in the latter, especially DPF loading status prediction.;The model was validated using the data gathered at the West Virginia University Engine and Emissions Research Laboratory (WVU-EERL) using a model year 2004 Mack MP7-355E Diesel engine coupled to a Johnson Matthey catalyzed diesel particulate filter (CDPF) exercised over a 13 mode European stationary cycle (ESC) followed by two federal transient cycles (FTP). A constant set of model tuning parameters were maintained for the sake of general validation of simplifying assumptions of the 1-D code.;The analysis shows that the predicted pressure drop across the DPF is in good agreement with the data obtained at EERL in both steady state and transient cycles. It is also shown that the soot accumulates mainly in the frontal and rear parts across the filter length under given soot concentrations. The model is capable of tracking DPF soot mass satisfactorily with a maximum discrepancy of 3.47g during steady state cycle. A 7.95% decrease in soot layer thickness can be seen in the front portion of the DPF during the transient cycle mainly due to O2 assisted regeneration at elevated temperatures. Both 1-D and 2-D models produce similar results during the loading phase. However, the current model is able to capture regeneration phase of the FTP cycle more descriptively than the 1-D model. The discrepancy of the reported total soot mass estimation between two models was 2.12%. The distribution corresponding to the 1-D model is representative of soot layer distribution given by the 2-D model at one tenth distance away from the DPF front face. 1-D model representation is effective towards PM prediction, although presenting considerable axial effects at higher DPF temperatures

디젤 엔진에서 가상 질소산화물 센서에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2013. 8. 민경덕.thus, this model can be applied to engines and after-treatment systems as a useful tool to control the engine-out NO without the use of a NOx sensor. In addition to being a virtual NO sensor, the estimation model can be applied to 1-D simulations, such as GT-SUITE and AMESIM, and demonstrate improved NO estimation results as the model is able to predict the NO level as same standard as the 3-D CFD simulation. Then, a newly developed NO estimation model was implemented on the embedded system bypassed from a conventional engine control unit for real-time estimation of NO during steady-states and transient engine operations. The results of the model were compared to real-time measurement of engine-out NO of a conventional Diesel engine at representative steady state operating points which cover the entire NEDC region. Also, EGR rate and main injection timing were varied to verify the predictability of the model under various conditions. The results showed that the model predicts steady state results well with R2 value of 0.96 for 76 HP-EGR cases. In addition, to verify transient estimation of NO, the engine-out NO was measured by a fast NO analyzer and compared with the results of the model during simple ramp transition conditions. Additionally, the engine-out NO emissions measured by a fast NOx analyzer and the estimated NO emissions were compared during ECE-15 and EUDC cycles. Furthermore, to extend the NO model to a complete NOx estimation model, an empirical NO2 estimation model was proposed based on the experiments under steady-state conditions. The in-house EGR estimation model was also applied in the NOx estimation model for accurate cycle-by-cycle estimation and used as an input during transient engine operations. This systematic research on the development of a virtual NOx sensor contributes to real-time NOx monitoring for transient NOx control and after-treatment system control.however, there were several limiting factors, such as complexity of the model for a real-time application, the necessity of various calibration constants, fitting processes for empirical equations and the demand for training for numerical models. In this study, to overcome the limits of previous studies, a real-time nitric oxide estimation model was developed based on the in-cylinder pressure and on data available from the ECU. As computational fluid dynamics can describe the process of NO formation which is not directly obtainable from experiments on a physical basis, the NO formation model was developed based on both the analysis of CFD results as well as on a physical model. Furthermore, the in-cylinder pressure is used to predict the amount of NO formation under various engine operating conditions as the pressure reflects the change in the combustion characteristics. The estimation model consisted of a simple calculation processTo meet the stringent emission regulations on diesel engines, engine-out emissions have been lowered by adapting new combustion concepts such as low-temperature combustion and after-treatment systems have also been used to reduce tailpipe emissions. To optimize the control of both in-cylinder combustion and the efficiency of an after treatment system to reduce NOx, the amount of real-time NOx emissions should be determined. Thus, many studies on a virtual NOx sensor using physical and phenomenological models have been reported. Previous studies have shown reliable NOx estimationstherefore, the model could predict the cycle-by-cycle NO in real-time. The validation results show that the model presented can predict engine-out NO well디젤 엔진에 대한 배기 규제가 강화됨에 따라 새로운 연소 기법을 이용하여 엔진 자체의 배출물을 줄이거나 후처리 장치 등을 이용하여 최종 배출물을 줄이는 등의 노력이 이루어지고 있다. 특히, 질소 산화물 (NOx) 감소를 위한 실린더 내 연소제어, 동시에 후처리 장치의 효율을 최적화하기 위해서는 실시간으로 배출되는NOx 배출량에 대한 정보가 필요하다. 따라서 물리적, 현상학적 모델을 사용한 가상 NOx 센서에 대한 많은 연구가 보고되고 있다. 기존 연구들은 비교적 정확하게 NOx 배출량을 예측하고 있지만 실시간 애플리케이션으로써 활용하기에는 현재 차량에 장착 중인 엔진 제어 장치의 계산 능력에 비해 모델이 너무 복잡하거나, 경험식을 피팅하기 위해 많은 보정 상수가 사용되고, 통계적 수학적 모델 등의 경우에는 많은 트레이닝이 필요한 등의 여러 가지 제한 요인이 있었다. 본 연구에서는 선행 연구의 한계를 극복하기 위해 실시간 실린더 압력과 ECU에서 얻을 수 있는 데이터에 기반한 실시간 NOx 예측 모델을 개발하였다. CFD 는 실험 과정에서 직접 얻을 수 없는 NO의 형성 과정을 자세히 설명 할 수 있기 때문에, 물리적 분석과 함께 CFD 결과의 분석을 통해 모델을 개발하였다. 또한 실린더 내 압력이 엔진 연소특성의 변화를 잘 반영하기 때문에, 다양한 엔진의 작동 조건에서 NO의 배출량을 예측할 수 있도록 연소압력이 사용되었다. 개발된 NO 예측 모델은 간단한 계산 과정으로 이루어졌기 때문에 실시간으로 사이클 별 NO를 예측할 수 있었다. 검증 결과는 제안된 모델이 엔진에서 배출되는 NO 를 잘 예측하는 것을 보여주었고, 따라서 개발된 모델이 NO센서 대용으로써 엔진과 후처리 장치의 제어를 위한 유용한 도구로써 시스템에 적용될 수 있음을 확인하였다. 가상 NO 센서로 사용될 수 있는 것 이외에도, 개발된 NO 예측 모델은 GT-SUITE와 AMESim 과 같은 1 차원 시뮬레이션에 적용되어CFD 모델과 동일한 수준으로 NO 수준을 예측할 수 있는 가능성을 가지고 있다. 이후, 개발 된 NO예측 모델은 정상 상태와 과도 엔진 작동 상태에서 NO의 실시간 추정을 위한 기존의 엔진 제어 장치를 우회한 임베디드 시스템에 구현되었다. 모델의 결과는 NEDC 전 영역을 커버하는 대표적인 정상 상태의 동작 점에서 엔진에서 배출되는 실시간 NO 측정값과 비교되었다. 또한 다양한 조건에서 모델의 예측성을 검증하기 위해 배기가스 재순환율과 주분사시기를 베이스 조건 대비 변화시켰다. 정상상태 검증 결과 HP-EGR 76 케이스에서 실험 결과와 R2=0.96 의 높은 예측 정도를 확인할 수 있었다. 또한 과도상태에서의 NO 예측 정도를 검증하기 위해 고속 NOx 분석기를 사용하여 엔진 속도, 부하 변경 등의 간단한 램프 조건에서 모델 결과와 비교하였다. 또한 유럽의 배출가스 측정 모드인 ECE-15 와 EUDC 사이클에서 고속 NOx 분석기 결과를 사용하여 모델을 검증하였다. 추가적으로, NO 만이 아닌 전체 NOx를 예측할 수 있도록 정상상태 실험 결과 기반의 경험식을 사용한 NO2 예측 모델을 제안하였다. 실시간 NOx 예측 모델에 정확한 과도상태 EGR 값을 제공하기 위해 실험실에서 개발된 EGR 예측 모델 또한 적용 되었다.Acknowledgements iii Abstract iv Contents vii List of Tables x List of Figures xi Acronym xiv Chapter 1. Introduction 1 1.1 Background and Motivation 1 1.1.1 Nitrogen oxides formation 1 1.1.2 The effect of nitrogen oxides on health and environment 2 1.1.3 Nitrogen oxides emission from diesel engines 3 1.1.4 Emission regulations for NOx from diesel engines 4 1.1.5 NOx reduction technologies and challenges in diesel engines 6 1.2 Literature Review on virtual NOx sensors 23 1.3 Objectives 28 Chapter 2. Development of NO estimation model with in-cylinder pressure measurement 29 2.1 Computational model and validation 30 2.1.1 Computational model for the CFD simulation 30 2.1.2 Validation of the computational models 30 2.2 NO estimation model 36 2.2.1 Basic assumptions for the NO estimation model 36 2.2.2 Physical model for NO formation 36 2.2.3 Determination of the duration of NO formation 39 2.2.4 Determination of averaged NO formation rate 39 2.2.5 Calculation of the maximum NO formation rate 40 2.2.6 Summary of the NO estimation model 43 2.3 Model validation with CFD results 53 Chapter 3. Experimental Apparatus 55 3.1 Engine setup 55 3.2 In-cylinder pressure measurement 61 3.3 EGR measurement 63 3.4 NO and NOx measurement 65 3.5 Real-time calculation of NO 68 Chapter 4. The effect of EGR rate on NO estimation model 72 4.1 Sensitivity analysis 72 4.2 Cylinder-to-cylinder measurement of EGR 74 4.3 EGR estimation model 76 Chapter 5. NO estimation during steady state and simple ramp transition using a real-time virtual NO sensor 82 5.1 Experimental cases 83 5.1.1 Steady state cases 83 5.1.2 Simple ramp transition cases 83 5.2 Experimental results 85 5.2.1 Steady state results 85 5.2.2 Simple ramp transition results 85 5.2.2.1 EGR rate change 85 5.2.2.2 Engine speed change 86 5.2.2.3 Simultaneous engine speed and load change 86 5.2.3 Source of error 86 5.2.4 Improvement of model accuracy using modified R and k 87 5.2.5 Cycle-by-cycle & cylinder-by-cylinder NO estimation 89 Chapter 6. NOx estimation during transient state using a real-time virtual NOx sensor 99 6.1 Extend to NOx (NO2) estimation model 100 6.2 Experimental conditions 105 6.3 Results and discussions 107 Chapter 7. Conclusion 113Docto