TEI-PD170-DT Turbodiesel Aviation Engine Through the Eyes of an Engineer

Developed by TUSAŞ Engine Industries Inc. (TEI) with the support of the Presidency of Defense Industries (SSB), Turkey`s first domestic and national turbodiesel aviation engine, the PD170, is considered as one of the best diesel aviation engines in its class, based on its power/weight ratio.

Date: Issue 108 - July 2021

Developed to power Medium-Altitude Long-Endurance (MALE) Class Unmanned Aerial Vehicles (UAV), the TEI-PD170 diesel aviation engine is very light thanks to the cylinder block and cylinder head cover made of aluminum alloy. Following the acquisition of high-temperature strength and wear resistance aluminum alloy technology as part of the AYNA Project signed between the SSB and İTÜ-İTÜNOVA TTO, and VIG Metal, the domesticity rate of engines has reached very high levels. When we look at the cylinder head cover of the new generation DCI type engine with Common Rail technology and completely managed by a domestic and national Electronic Control Unit (ECU), we see that it has a double overhead camshaft (DOHC) mechanism. Since TEI-PD170 is planned to power the aircraft, a timing belt is preferred to drive the camshaft instead of gear, chain, or shaft to be lighter. I believe that the exhaust valves are made of standard steel alloy, while the intake valves are made of titanium for the engine to provide more torque and power. Titanium intake valve springs are 3-4 times harder than standard valve springs. In this way, the camshaft cams close much faster when the pressure on the intake valves is terminated, thus minimizing the leakages.

TEI-PD170-DT (Dual Turbo), which has very efficient fuel consumption, has 4 cylinders with a total volume of 2,100cc. Compared to the TEI-PD180-ST (Single Turbo) engine, which has one large-diameter turbocharger but is 10kg lighter and 10hp more powerful at sea level, the TEI-PD170-DT has 2 serial-connected turbochargers (two-stage turbocharging) to maintain the power it produces at high altitudes. The reason for choosing a serial turbocharging system is that the air compressed by the first turbocharger is then further compressed by the second turbocharger so that the engine is less affected by the low oxygen amount at high altitudes. If parallel turbocharger configuration were preferred, the "headers" (exhaust manifolds) shared by the 4 cylinders would be divided into two, and the exhaust gas pressure would be shared halfway between the two turbochargers. In this case, due to the small volume of the engine, the exhaust gas pressure would not be able to rotate the turbine blades at sufficient speed, and the engine would lose power. Smaller diameter turbochargers could be used to prevent this, but in this case, since the diameter of the snail fans would also get smaller, the compressor output would also decrease, and nothing would change. Therefore, only a serial turbocharging system can be used. All turbochargers used on the TEI-PD engine family also have a "wastegate" system. In short, this is a security system that regulates the maximum boost pressure in turbocharger systems to protect the engine and the turbocharger. The turbine blades, which operate at around 600°C and are under a great load due to centrifugal force, reduce their efficiency by changing their angle to allow excess exhaust pressure to bypass the turbine and limit their rotational speed. It is not difficult to estimate the load on turbine blades rotating at 200,000 RPM (revolutions per minute) due to centrifugal force. However, when turbochargers without a "wastegate" system are used, the engine's power output will be much higher. While the turbocharger on the 172hp TEI-PD170-DT engine has a typical boost pressure of 0.9 – 1.8 bar, the TEI-PD222 engine, which was increased to 2.0 – 3.0 bar, provides more power and torque, and the power-to-weight ratio has been improved further. There is also a model named TEI-PD222-ST that is 10kg lighter with a single turbocharger. From PD155 to PD222-ST, all engines in the expanding diesel engine family developed by TEI have in-line cylinder block arrangements. Compared to V or VR type engines, in-line engines stand out with their ease of production and lower cost advantage.