Aşırı doldurmalı ağır hizmet motorunun hava yolu kontrolü ve uygulaması
Mass air flow control and application of a turbocharged heavy duty diesel engine
Yazar: OSMAN UYGUR
Danışman: PROF. DR. LEVENT GÜVENÇ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Mekatronik Mühendisliği Ana Bilim Dalı / Mekatronik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Makine Mühendisliği = Mechanical Engineering ; Mekatronik Mühendisliği = Mechatronics Engineering
Dizin: Dizel motorlar = Diesel engines ; Egzoz emisyonları = Exhaust emissions ; Otomotiv = Automotive ; İçten yanmalı motorlar = Internal combustion engines

Özet:
2016 yılından itibaren ülkemizde de uygulanacak olan Euro VI emisyon regülasyonunun gerektirdiği NOx limitleri, sadece yakıt sisteminde yapılacak zamanlama ve basınç gibi parametre optimizasyonları ile sağlanamayıp, aynı zamanda EGR, DPF ve SCR gibi farklı uygulamaların kullanılmasını zorunlu hale getirmektedir.Bu çalışma kapsamında hali hazırda Euro I-III-IV-V emisyon regülasyonlarını sağlayan aşırı doldurmalı bir ağır hizmet motoru, Euro VI emisyon regülasyonunu sağlaması için prototip parçalar kullanarak EGR sistemi ve hava kelebeği ile donatılmış, NOx emisyonlarının düşürülmesi amacıyla kütle hava akışı kontrolü yapılmıştır.Birinci bölümde, tezin konusu, kapsamı ve amacı hakkında genel bilgiler verilip, kullanılan motor tanıtılmıştır. Kütle hava yolu kontrolü yapılacak prototip motor üzerindeki ölçüm noktaları gösterilerek kütle hava akışı kontrolünde nelerin kritik olduğu anlatılıp, EGR sistemi ve hava kelebeği hakkında bilgiler verilmiştir. Literatürde kütle hava akışı kontrolü metodları üzerine araştırma sonuçları paylaşılıp, kontrolcü hakkında genel bilgiler verilmiştir.İkinci bölümde, bu çalışma kapsamında kullanılan motorun hava yolu tanıtılmıştır. Motor üzerindeki aşırı doldurma sistemi ile birlikte prototip parçalar kullanılarak motor üzerine takılan EGR sistemi ve hava kelebeği komponentleri tanıtılarak karakteristikleri hakkında bilgi verilmiştir. Bu komponenetler kullanılarak gerçekleştirilen test sonuçları paylaşılmış, hava yolundaki basınç değişimleri ve NOx emisyonlarına etkileri gösterilmiştir. Ayrıca, Euro VI emisyon regülasyonu testleri hakkında bilgi verilerek, motor haritası üzerinde gösterilip yorumlanmıştır.Üçüncü bölümde hava yolu kontrolü yapmak için gerekli olan EGR valfi ve hava kelebeğinin kapalı çevrim kontrolü kullanılan metodlar ve haberleşme yapıları ile anlatılmıştır. Hedeflenen ve ulaşılan değerler arasındaki farklar incelenip, kütle hava akışı kontrolcüsünün genel yapısı hakkında bilgi verilmiştir.Dördüncü bölümde, hava yolu kontrolü yapmak için kullandığımız cihazların ve sensörlerin birbirleri ile olan iletişimi anlatılarak, birbirinden farklı yapıda olan bu cihazların nasıl bir arada çalıştırıldığı anlatılmıştır. Bu sistem ile koşulan test sonuçları paylaşılarak, tasarlanan kontrolcünün nasıl çalıştığı gözlenip, EGR valfinin ve hava kelebeğinin pozisyonları gösterilmiştir.Son bölümde ise mekanik, elektronik, kalibrasyon ve kontrol, sensörler ve analizörler açısından sonuçlara ve önerilere yer verilmiştir.

Abstract:
With increasingly stringent emissions regulations, especially for nitrogen oxides, emission control using only injection parameters has become insufficient and application of additional technologies and new technologies for engine development has become necessary.European emission regulations standardize the applicable limits for carbon monoxide, hydrocarbon, nitrogen oxide, particulate matters and smoke. These limits were first introduced as Euro I levels in 1992 where the NOx, PM, CO and HC limits were implemented. Since then, emission limits have been updated every 3-5 years. Currently, Turkey enforces Euro5 limits where the emission limit is 2 g/kWh for NOx. In 2014, Euro VI emissions will be introduced for the first time across Europe and some of the neighbouring countries. In Turkey, these limits will come into effect in 2016. These limits, compared to those of Euro I, represent a 95% reduction in NOx. Heavy-duty Euro VI emission levels, tests and other diagnostic information are based on 595/2009/EC directives. Most challenging emission level is nitrogen oxides, which is regulated as 0.4 g/kWh, previously 2 g/kWh at Euro V emissions.Emission regulations depends on vehicles tonnage and reference weights greater than 2610 kg classified as heavy duty vehicles. Heavy duty emission regulations are stricter than light duty and passenger can emission regulations, because of this situation diesel engine and emission technologies focus on heavy duty engines within last years. There are many ways to reduce nitrogen oxides emissions, which is the most challenging one. Using injection timing optimization, using higher rail pressure and exhaust gas recirculation is the main parameters for engine out nitrogen oxides emissions. Using exhaust gas recirculation system can cause high particulate matter. To avoid of this situation, high rail pressure is required for better combustion for engines with EGR system.Aftertreatment technology is also very important to achieve Euro VI emission limits. Aftertreatment components are Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), and Selective Catalytic Reduction (SCR). DOC is required for burning fuel at the exhaust to start regeneration at the DPF. DPF is mendatory to achive particulate matter limits, which is 0.01 g/kWh and particul number limits, which is 6× ? 10 ? ^11 #/kWh. Using selective catalytic reduction and exhaust gas recirculation technology together is a way to achieve nitrogen oxides limit.In the scope of this project, a turbocharged engine, which is compatible with Euro-I-II-III regulations, is equipped with air intake throttle valve and EGR system in order to make it suitable to engine out Euro VI emissions. By positioning EGR valve and air intake throttle valve, mass airflow can be controlled and required EGR rate satisfied.In Heavy Duty trucks with fixed geometry turbochargers, it has been shown that even with the EGR valve fully open, EGR may not flow under all circumstances to ensure compatibility with Euro VI emissions standards, thus requiring the use of an air intake throttle valve to further assist EGR flow. Basic principle of a high pressure EGR system is letting exhaust gas in to cylinders. This condition needs pressure difference between intake and exhaust manifolds. Negative pressure difference of boost pressure and EGR cooler outlet pressure satisfies the EGR flow, else is not possible. Because of turbo characteristics, this difference may not big enough for some points at engine map to flow enough exhaust gas in to the cylinders; even reverse flow could be possible.At normal condition using an air intake throttle valve is not expected at diesel engines, if used, general usage area is increasing temperature at engine out gas temperatures for regeneration. In this study, throttling used for additional pressure drop at the intake system. This condition generates pressure difference across the exhaust and intake manifolds so that, exhaust gas flow can flow in to cylinders. However, this condition increases specific fuel consumption. Thus, air intake throttle valve should not be used unnecessarily.There are of course other technologies which can be used to get a similar result as using air intake throttle valve. An example of such a technology is Variable Geometry Turbocharging (VGT) wherein the same boost pressures required and attained by a Fixed Geometry Turbo (FGT) can be achieved by a smaller turbo, resulting in a higher delta pressure across the EGR system. As it is this pressure difference which drives the EGR flow, a similar result to throttling can be realized in terms of the increase in EGR flow. However, the VGT technology has a large cost penalty and in light of the importance of cost effective engines and due to competition, this is an on-cost which is usually not acceptable.In the first part, the purpose of thesis and topic are provided and engine that is used for the project is explained. Measurement points on the prototype engine are shown and what is critical in mass airflow control is clarified. Air path control is mandatory to achieve Euro VI emissions and EGR system is one of the key components for this. Typical systems for airflow control are Exhaust Gas Recirculation (EGR), air intake throttle valve and variable geometry turbocharger. In this thesis, fixed geometry charged turbo is used, EGR valve and air intake throttle valve is used for air path control. EGR rate measurement principle is explained for understanding exhaust gas flow rate in to the cylinders. Besides, EGR system and throttle valve are defined, the results of different researches on mass airflow control and general information about controller are shared. Various tests are performed to understand the characteristics of the air path of the engine. These tests performed by using high precision sensors and analyzers.In the second part, air-path of the engine is described. Turbocharged engine with prototype EGR system and throttle valve and its characteristic are explained. Test results of these experiments are shared and pressure change in air path and its effects on nitrogen oxides emissions are depicted. EGR rate, which is critical for nitrogen oxides emissions, calculation and characteristics with respect to throttle valve position described. Furthermore, European Emissions Regulations are explained, including details about the Euro VI emissions regulation, the drive cycle used to evaluate the emissions and its general residency areas, followed by pre-experiments. Euro V emission cycles and Euro VI emission compared and it is shown that Euro VI transient emission cycle is more aggressive. The relationship between nitrogen oxides emissions and mass airflow is further explained, and data at various engine rpms is shared. Measurement instrumentation points used in these tests and the formulation to calculate EGR rate from these is also detailed. This prototype engine is equipped with various sensors and analyzers. Measuring pressures and temperatures at the air path is important to understand EGR flow characteristics. For this reason, intercooler outlet pressure, boost pressure, EGR cooler outlet pressure, intake and exhaut manifold oxygen and nitrogen oxides levels online monitored and recorded.In the third part of this thesis, steps for the design of closed loop controllers for the EGR and intake air throttle valves is detailed, followed by a controller for closed loop mass air flow control. CAN communication and database explained for EGR valve and closed loop actuator control performed for air intake throttle valve. Air intake throttle valve controlled via H-Bridge DC motor driver and PID controller. Setpoint and measured position of the actuator recorded and compared. Mass airflow control, which is the main part of this thesis, is also described in this section. PID controller used and this block is the fundamental control logic. The input to the controller is the error signal, which is the difference between demand and measured mass air flow. PID controller outpus is generated by summing the outputs and the error signal, which is fed to proportional, integral and sometimes derivative terms, which is not used in this study. Not only calibrating mass airflow controller, proportional, integral and derivative terms correctly, but also closed loop EGR position control and air intake throttle valve control has to be working correctly for mass airflow control. Air intake throttle valve should only be used when EGR rate is not enough to meet nitrogen oxides emissions while the EGR valve is fully open. Minimum and maximum functions used for activating air intake throttle valve only if the EGR valve position is fully opened. Air intake throttle valve should have a maximum position to avoid of smoke at exhaust because of less air.In the fourth part of this thesis, application of the mass airflow control performed and results are shared. One steady state and one transient test performed and EGR valve position, air intake throttle valve position, mass airflow, error and emission results observed. Communication structure of different kind of devices is also detailly explained. AVL Puma system is used for controlling speed, torque, EGR valve and air intake throttle valve positions, sensors and analyzers. However, EGR valve and intake air throttle valve setpoints are calculated by controller, which runs at dSpace MicroAutoBox, and feed directly to AVL Puma system. PI and feed forward parameters can be calibratible via dSpace ControlDesk and observing system response online is possible. These parametres also determined in this section. Determining PI parameters for the points at engine map could cause a high calibration effort due to engine characteristics difference at the engine map. Thus, only a few important points at the engine map calibrated and tested due to engine and the parts are prototype. However, same steps can be followed for entire engine map.In the final part, results in the respect of mechanical, electronical, calibration and control, and sensor and analyzer are provided and suggestions are presented. Dynamometer tests shows that, turbo charged system that used on standard diesel engines cause high intake manifold pressure on some WHSC and WHTC points, and this situation effect EGR flow negatively. Using air intake throttle valve solves this problem with fuel economy penalty.