Aşırı doldurmalı ağır vasıta motorunda reed valf deneysel uygulaması
Experimental application of reed valve on turbocharged heavy duty engine
Yazar: ALİ YALÇIN
Danışman: DOÇ. DR. OSMAN AKIN KUTLAR
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Bilindiği gibi dizel ağır vasıta motorları için emisyon kısıtlamaları yıldan yıla artmaktadır. 2016 yılından bu yana ülkemizde yürürlükte olan EU VI/6 emisyon kısıtlamaları EU 6-d ve EU 6-e olarak güncellenmiştir. EU6 sonrası emisyon kısıtlamalarının özellikle EU7 ve sonrası için artararak artacağı beklenmektedir. 2025 yılında EU7 standartlarının yürürlüğe girmesi beklenmektedir. NOX gibi zehirli gazların yalnızca genel limitleri kısılmayacak aynı zamanda test yapılan çerçeve de genişletilecektir. Bu sayede, yapılan testler gerçek yol sürüşlerini daha çok kapsar hale getirilecektir. Örneğin soğuk çevrimde motor ısınmadan NOX limitlenmesi gibi. EU7 sonrası için ise Avrupa Birliği Komisyonu tarafından açıklanan önce nötr sonra da sıfır karbon politikasının 2030 ve 2050 yıllarında devreye girmesi beklenmektedir.
EU6 emisyon seviyesine sahip bir motor ve egzoz sistemleri, yeniliğe gitmeden yalnızca kalibrasyon geliştirmesiyle bir sonraki çok kısıtlı emisyon değerlerini sağlaması mümkün görülmemektedir. Hali hazırda Eu6-e emisyon standartlarını sağlayan Ford Otosan firmasına ait 12.7 litre ağır vasıta motorunda, EU6 sonrası (EU7) NOX kısıtlamaların karşılanabilmesi için prototip fazda çalışmalar yapılmıştır.
NOx emisyonunu azaltmanın en etkili yolu egzoz gazlarının bir kısmını tekrar manifolda beslenme prensibine dayalı EGR sisteminin kullanılmasıdır. Bu sirkulasyonun, valf zamanları ile ayarlanarak iç EGR sistemi, ya da egzoz sisteminden emme manifolduna borulama yapılarak harici EGR sistemi olarak endüstride kullanımı mevcuttur: yüksek basınçlı, düşük basınçlı, karma ve reed valf kullanılan EGR sistemleri gibi.
Yüksek basınçlı EGR sistemlerinde eğer sistemde harici bir EGR pompası yoksa -ki test motoru yüksek basınçlı EGR sistemine sahiptir ve EGR pompası yoktur- EGR akışı doğal olarak türbin girişindeki egzoz gaz basıncının, emme manifoldundaki gaz basıncından yüksek kalabildiği şartlarda elde edilebilir. Oysa motor haritasında her noktada bu fark pozitif oluşmaz ve EGR doğal olarak akamaz.
Tez kapsamında tam da bu soruna yönelik olarak, standart EU6 motora iki yollu EGR ve reed valf (tek yollu vana) montajı yapılmıştır. Reed valfin amacı, egzoz gazı sistemi ile temiz hava sistemi arasındaki bağlantıyı valf öncesi ve sonrası basınçtan bağımsız olarak açmak veya kapatmaktır.
Deney noktaları, ağır vasıta sertifikasyonu için gerekli olan WHTC testinde en sık durulan bölgeden türetilmiştir. Sonuç kısmında 1000 rpm motor hızı ve görece düşük motor momentlerinden tam yük bölgesine doğru EGR valf pozisyon taramalarını detaylıca paylaşılmıştır.
Tez kapsamında yapılan deneylerde, negatif basınç farkı bölgelerinde (Emme manifold basıncının egzoz basıncından yüksek olduğu) EGR akışını mümkün kılarak NOX azaltma hedefine ulaşılmıştır ve bu tez EU6 sonrası motor ve egzoz sistemleri geliştirme projelerine ışık tutacaktır.

Abstract:
As it is known, emission restrictions for diesel heavy duty engines are increasing from year to year. EU VI/6 emission restrictions in force in our country since 2016 have been updated as EU 6-d and EU 6-e. Post-EU6 emission restrictions are expected to increase, especially for EU7 and beyond. EU7 standards are expected to come into force in 2025. Not only will the general limits of toxic gases such as NOX be reduced, but the testing framework will also be expanded. In this way, the tests will be made more inclusive of real road driving. For example, NOX limitation in cold cycle without warming up the engine. For post EU7, it is expected that the neutral and then zero carbon policy announced by the European Union Commission will come into effect in 2030 and 2050.
Within the scope of this thesis, air path analysis of heavy-duty vehicle diesel engine was made. As mentioned above, studies aimed at reducing NOX gas thrown into the atmosphere were planned without making any changes in the engine combustion chamber or on the fuel path, and the dual-way EGR and Reed Valve were integrated into the air path system. The reed valve does not have any control system on it and is designed to allow one-way flow to catch the pressure waves in the exhaust gas.
In this way, without using any extra control parts (such as the EGR pump), EGR has been obtained in different operating regimes of the engine with minimum cost increase and NOx has been reduced. With the studies carried out within the scope of the thesis, steps have been taken to meet the future EU7 emission standards for the heavy vehicle diesel engine that currently meets the Eu6 emission standards.
An engine and exhaust systems with an EU6 emission level would not be able to achieve the next very restricted emission values by only improving calibration without innovation or adding new components. Prototype phase studies were carried out in order to meet the post-EU6 (EU7) NOX restrictions on the 12.7-liter heavy vehicle engine of Ford Otosan, which currently meets the Eu6-e emission standards.
The most effective way to reduce NOx emissions is to use the EGR system based on the principle of feeding some of the exhaust gases back to the manifold. This circulation is used in industry as an internal EGR system by adjusting the valve timings, or as an external EGR system by piping from the exhaust system to the intake manifold: EGR systems with high pressure, low pressure, mixed and reed valves.
In high pressure EGR systems, if there is no external EGR pump in the system – the test engine has a high pressure EGR system and no EGR pump – the EGR flow can naturally be obtained under conditions where the exhaust gas pressure at the turbine inlet can remain higher than the gas pressure in the intake manifold. However, this difference is not positive at every point on the engine map and the EGR flow cannot be obtained .
In this thesis, two-way EGR and reed valve (one-way valve) have been installed on the standard EU6 engine for exactly this problem. The purpose of the reed valve is to open or close the connection between the exhaust gas system and the clean air system, regardless of the pressure before and after the valve. 
A reed valve is a valve system that allows gas flow in only one direction. When a pressure difference occurs in the system that may cause reverse flow, the valve closes and does not allow flow. Exhaust gas has a very pulsating, bumpy flow. Thanks to the reed valve, it is aimed to benefit from all of these pressure waves. Every time the exhaust gas pressure exceeds the manifold pressure, the valves open, resulting in a significant increase in the EGR rate. In cases where there is a negative pressure difference (where the manifold pressure is higher than the exhaust pressure), the valve closes and the EGR cooler also closes. Reed valve is generally installed in the system after the EGR cooler.
In the third part of the thesis, information is given about the history of emission restrictions from EU1 until today and possible emission restrictions after EU6. The workshops of ACEA and the European Union Commission were discussed and possible post-EU6 solutions were discussed.
For EU VI/6 emission restrictions, restrictions can be achieved by integrating DOC, DPF, SCR, urea injector, external fuel injector into the after-engine exhaust systems. Possible cold zone and very low working load restrictions in post-EU VI emission limits can be solved by adding 12V E-CAT (electrical catalyst) to the standard system. Since the exhaust gas will be very cold at very low loads, it cannot operate at full efficiency and NOX limits cannot be achieved. NOX conversion is facilitated in low load and cold cycles with an external 12V system. For EU VII / 7 and beyond, a low NOx target is expected at all operating points. Therefore, improvements only to low load zones or constant speed zones will not be sufficient. The new constraints cannot be solved only with calibration improvements, and even the 12V E-CAT shown above will not be enough. There are approaches that foresee the use of double urea dosing system and both high pressure and low pressure EGR systems for the solution.
Since the NOx restriction in the EU7 emission limits will increase much compared to the previous legislation, the reed valve, which is a low cost but effective system to be built on the standard EU6 engine, has been tested in this thesis.
In the 4th chapter of the thesis, the data collection systems used in the tests performed on the dynamometer and briefly their working principles are given. Such as NOX emission measurement, air and fuel flow measurement, and pressure and temperature measurement.
In the 5th part of the thesis, test setup scheme, experiment scope, experiment steps and results are shared in detail.
Fixed geometry and two-line turbo system and reed valve were installed on the 6-cylinder heavy duty engine of Ford Otosan. The exhaust system consists of two lines, the exhaust line coming out of the cylinders 1-2-3 after the manifold and the exhaust line coming out of the cylinders 4-5-6. The exhaust gases come to the EGR cooler through a double line, and the cycle is completed as a single line over the reed valve and mixed with the clean air and enters the intake manifold.
The procedure to be done before the tests to be carried out after the assembly phase is to determine the volumetric efficiency of the test engine.
The electronically controlled EGR valve has been brought to the fully closed position from calibration and is physically blocked from where it is connected to the intake manifold. In this way, the maximum amount of clean air that the test engine can receive was determined. One of the most critical steps for the accuracy of the calculated EGR amount is to correctly determine the volumetric efficiency. For this reason, the EGR valve was not only brought to a closed position on the controller, but also physical blocking was applied to prevent leaks. The amount of fresh air entering the engine during the test was subtracted from the predetermined maximum amount of clean air, and the amount of EGR gas at that point was determined.
In this experiment, steady satate tests were carried out at different loads at constant engine speed. Approximately 15 different EGR positions were sweeped in each load. These are the points where there is no natural EGR flow in the standard engine. In other words, the points where the intake manifold pressure of the engine is higher than the turbine inlet pressure are the operating points.
The most frequently used points in the WHTC emission test were determined and included in the test. The engine torque range of 800Nm and 1800Nm was sweeped at 1000rpm engine speed. Improvements that can be made at these points will inevitably have a large impact on WHTC.
In the experiments conducted in the thesis, the target of NOX reduction has been achieved by enabling EGR flow in negative pressure difference regions (where the intake manifold pressure is higher than the exhaust pressure), and the results of this thesis make a difference to the development projects of engine and exhaust systems after EU6.