T-72/T-90 and T-80 engine cooling

This article is a simplified approach to explaining how Soviet/Russian engines are cooled. 

The T-72 and T-90 series of vehicles are equipped with standard V-84 and V-92 engines. Both engine types feature an enclosed liquid cooling loop with active air-cooling circulation facilitated by a fan. 

The T-80 and its GTD series of engines, including the GTD-1000 and the GTD-1250, utilize active air and oil cooling for the turbine.

DETAILED LOOK AT THE T-72/T-90 ENGINE COOLING LOOP

T-72 engine cooling loop and layout

The T-72 uses a closed liquid loop system to cool the engine and two oil lubrication tanks. Coolant heated by the engine is divided into three streams within the engine bay: 

The main coolant stream is pumped into the radiators and cooled with atmospheric air, which is pulled into the engine bay using a ventilator. After passing through the radiators, the coolant enters the engine water pump.

The second stream flows towards various components, such as the coils inside the engine's main oil lubrication tank and the hydraulic control and lubrication system tank, which lubricates the transmission. The flow also reaches the heating unit, which is mainly used during winter. 

The third stream circulates through the drainage and compensation circuit, which is directly connected to the heads of the engine block. It also circulates through the left water radiator before entering the water pump.

T-72 cooling fan drive and layout 

As for the cooling fan in the T-72 and T-90 series of tanks, the fan is powered by diverting a fraction of power from the engine. This is done with a transfer case, which transfers power from the engine to the left and right BKPs. The fan is mechanically coupled to a fan drive bevel gear connected to the transfer case. The fan has high and low operating modes. Per Vestnik data, a T-72 with a new cooling fan and inlet vanes (1984-1985), the cooling losses at high mode were 7.7% and 4.9 in low mode. Note that the % loss is from the total hp the engine outputs. 

DETAILED LOOK AT THE T-80 ENGINE COOLING SYSTEMS

GTD-1000T/TF and GTD-1250 air flow diagram. Red-black arrows indicate polluted air, red arrows indicate clean air circulating inside and around the engine block, and black arrows indicate sand and dust particles. More about GTD air filtration can be found here.

Unlike the V-84 and V-92 series of engines, the GTDs do not use a closed liquid cooling loop. Instead, the engine draws in atmospheric air, purifies it, and uses it to cool and supply vital engine modules. 

The engine has 2 separate air streams. The first stream directly supplies the engine and various sub-systems with air. This includes the main turbine, GS-18MO generator, AKS-150S and the GS-12T starter (modules used by GTD-1000T). The sub-systems do differ on the GTD-1250, but the supply of air is the same. A ventilator below the cyclones diverts part of the purified air to cool the aforementioned auxiliary units. 

A similar feature between GTDs and V-84/92 is that both engine bays have air circulating around the engine, which helps cool down external parts. 

The second stream is for cooling the engine lubrication loop. For this, the engine has 2 oil radiators located behind the cyclone filters. The left radiator is for cooling engine oil and the right radiator cools oil used for the BKPs. 

Diagram for the left oil radiator. The airflow principle also applies to the right radiator. 

To achieve steady airflow to cool the radiators, the monobloc comes with 2 blower fans, which actively suck in air through the radiators, cooling them, and dumping the warm air out of the engine via ducts. 

The ventilator and 2 blower fans are powered by diverting a fraction of the power directly from the turbine and not from a transfer case like on T-72. 

Mechanical diagram of GTD-1000T

Following the diagram, power is diverted from the central turbine shaft to the central drive shaft of the lower-pressure compressor. From there, it is transferred to a gearbox, which transfers it to the frontal transfer case. This transfer case powers both the blower fans and the ventilator. According to publicly available information, the GTD-1250s cooling system draws 40 hp. This value could be similar for GTD-1000T/TF with a possible margin of deviation. 

Engine comparison chart. GTD-1250 cooling system power draw rated at 40 hp.
From a short Soviet film about the GTD-1250. 

Lastly, turbine cooling. GTD turbines run at much higher temperatures than the V-84/V-92 series of engines. The GTD-1000T/TF and GTD-1250 are both air-cooled. Cooling air is generated by the low-pressure compressor and constantly pumped into the engine's chambers and cavities. High-pressure compressors provide large amounts of air, which fills air chambers and cavities, primarily around the combustion chamber. Air supplied by the high-pressure compressor enters the combustion chamber through the inlet slats to regulate combustion temperatures. 

Diagram depicting streams of air used to cool vital turbine components: low- and high-pressure turbine blades and external surfaces surrounded by cavities and chambers. 

The blades of low- and high-pressure turbines are major cooling points. One interesting feature is that the blades on the high-pressure turbine have air actively pumped through their inner cavity. This helps keep the blades cool enough to prevent structural degradation and wear. It's worth pointing out that the combustion chamber at its ignition point reaches temperatures of about 2500°C, which is achieved by forcing a large amount of air through the fuel injector. 

The hot high-pressure gases cool past the combustion chamber to about 950°C (GTD-1000TF) before reaching the aforementioned high-pressure turbine blades. These temperatures then gradually fall off as the gases go through the turbine. Low-pressure turbine blades at the very end of the turbine get cooled using a passive stream of air and do not have internal cavities. 

To conclude, Soviet/Russian diesel and gas turbine engines are not only vastly different in their designs and how they function but also in the way they are cooled. Diesel engines require less complex cooling systems, which are close to average non-military engines. With the complexity of gas turbine engines and generally much higher operating complexity, these machines require a lot more complex system to keep them running smoothly and preferably for a long time. 

It is worth mentioning that with the latest developments in domestic Russian GTD production, the possibility of making a more powerful GTD-1400 has been plausible, especially with the topic of increasing power output while retaining the same monobloc. More complex cooling and thermal regulation measures have to be implemented. 

Sources: 

1. Вестник бронетанковой техники 1985, Сборник Но.2 
2. Газотурбинный двигатель ГТД-1250. Филмь - Film 
3. Двигатель ГТД-1000Т. Техническое описание. МО СССР. Москва 1980
4. Двигатель ГТД-1000Т. Серия плакатов 
5. Система охлаждения Т-72
6. Танк Т-72Б Техническое описание. Москва Военное Издательство 2002
7. T-72 The Definitive Guide to the Soviet Workhorse". Ryan A. Then