The behemoth of all diesel engines designed and developed in India is now ready. The Prototype is tested for full power using the turbocharger made by GTRE.
The engine is probably one of the most important components of any moving vehicle including the main battle tanks (MBT). These powerplants aka engines should produce the required amount of power and torque to move a 50-60 tonne battle tank in different types of terrains and scenarios. To move these tanks, heavy capacity diesel engines are used which produce a lot of power and torque.
Before going into why only diesel engines are used and not petrol, we will discuss about the inherent advantages diesel as a fuel has over petrol engines.
- Diesel has a self-ignition property that petrol lacks.
- Diesel can work at leaner air-fuel ratios which makes them more efficient than petrol engines.
- Though diesel’s calorific value is slightly less than petrol’s, diesel is denser making the fuel more energy-dense by volume.
- Compression ratios of diesel engines are higher than petrol engines because of their resistance to knock and compression ratio is proportional to the efficiency of the engine.
- Because of resistance to knock, diesel engines can be designed to produce huge amounts of torque, which is required to move the vehicle, which is one of the main reasons why diesel as a fuel is preferred to move MBTs over petrol.
Till now, India has been importing or license making high capacity diesel engines from Russia and Germany. The power rating of these ranged from 700 to 1000 HP. MTU has been the supplier for the Arjun MBT engine and CVRDE has also uprated the current 780 HP engine that is being used in T-72 to 1000HP and is currently in the final stages of field testing.
Requirement for Indigenous engine
“No country has ever become a superpower over imported technology”. These words were spoken by Vijay Bhatkar, the architect of India’s first supercomputer. This urge of becoming a superpower drove DRDO to start development of high power 1500 HP engine to power FMBT (Future Main Battle Tank).
For developing this behemoth of an engine, DRDO formed a team comprising members from academia, user, industry and DRDO. A foreign consultant was roped in too to assist in the development of the engine and this could be AVL from Austria as CVRDE has used software’s like AVL BOOST to perform thermal simulations.
A lot of advanced technologies are being used to design and develop this engine. Let’s dive deeper into the technicalities and some of the sub systems that CVRDE has designed for this particular engine.
To achieve the high-power rating and better efficiency, CVRDE has concentrated mostly on three points.
1) Increase the BMEP
2) Increase the speed of the engine
3) Improving the efficiency of the engine
Brake Mean Effective Pressure if put in layman terms is the average pressure that the piston experiences during an engine cycle (intake, compression, power, and exhaust strokes). The more BMEP, the better will be the efficiency of the engine. This BMEP can be increased by increasing the charge density and reducing the air/fuel ratio.
Speed of the engine
Mean piston speed is the limiting factor for finalizing the engine speed. For these types of applications, engine with high piston speed are usually selected. It looks like CVRDE has used mean piston speeds of upto 14 m/s (meters/second) and in future this will be increased to 15.
Friction reduction techniques
In a technical paper that was published by CVRDE in July 2017 listed some of the friction reduction techniques to improve the efficiency. They are
1) Offset piston pin
2) Special coating on pistons
3) Reduction in tangential force on piston rings
4) Rolling element bearings for crankshaft and camshaft.
Though it is not clear whether all the above techniques were used, it is safe to assume that CVRDE might have used all of these as these are basic friction reduction techniques in “V” configuration engines. CVRDE is also researching on nano particles so friction reduction coatings can be used on pistons.
Air fuel ratio is the ratio of air to fuel molecules inside the cylinder. The stoichiometric ratio is 14.7:1 for diesel and as diesel engines are more efficient and can run leaner ratios as discussed above, these engines can be designed to run on leaner ratios. From a paper published in 2017, it looks like CVRDE is aiming to run the engine on ratios of 22:1.
Common Rail Direct Injection (CRDI) is one of the most advanced fuel injection systems currently available in the world. In this technology, the injection system consists of a Common rail or a pipe which supplies fuel under high pressures to the injectors from where the fuel is injected into the cylinder directly. The injection pressure CVRDE is using here is around 1600 bar. This system helps in atomizing the fuel completely and also helps in equal distribution of the fuel inside the cylinder.
Engine configuration is the configuration that defines the arrangement of cylinders inside the engine. For packing benefits CVRDE has used a V-12 arrangement with 90 degrees angle between the two cylinder banks.
Also, from the same paper, it can be assumed that the engine uses a cross-plane crank to make it a high revving engine. But cross-plane cranks are heavy and can hinder the power to weight goals. In the cross-plane crank, as shown below, the crank pins have a 90-degree angle between each other making the valve and injection timing more aggressive. I would say CVRDE went a bit crazy over here and used sports car technology.
Tangential intake runners
Intake runners supply the air to the engine. Generally tangential runners are employed in modern day engine to introduce swirl to the air while entering the cylinder. CVRDE has used CFD software ANSYS-Fluent to optimize the intake runners to provide the engine with sufficient air at all situations.
Turbo charger is a type of forced induction technique where air under pressure is forced into the cylinders to increase the amount of power produced. For the first time in its history, GTRE has designed and developed a turbocharger specially for this engine. A turbocharger contains two segments namely the turbine and the compressor. The exhaust gases from the engine enters the turbine housing where they spin the turbine.
This in turn spins the compressor which is connected by a common shaft to the turbine so that pressurised air is sent to the engine for more power generation. This Turbocharger also employees waste gate to control the boost pressure. GTRE has employed resistance welding in this turbo charger. In order to cool the hot air entering the cylinders, CVRDE has used an air-water cooling system to increase the density and decrease the temperature of air entering the engine.
Light weight construction
According to Newtons laws of motion, every body has a moment of inertia. IF we want to bring a machine to its optimum working conditions as soon as possible, it should have lower moment of inertia So CVRDE seems to have employed lighter material construction for moving parts especially piston, connecting rod, compressor and turbine blades, etc.
From another technical paper that was published by CVRDE in May 2017, it was mentioned that Grey cast iron was used to design the structural parts of the engine such as cylinder head. In this paper, the thermal, velocity and stress bearing performance of three head designs was analysed and results were compared. It was concluded that the curved head design (configuration 3) performed better than the other two. So, it is safe to assume that this configuration was used to design the head of this engine.
Air filtration system
According to the paper published in July 2017 by CVRDE, the average concentration of dust particles present in the Indian desert condition is of the order of 2 g/m3. So a two stage air filtration system was designed particularly for this engine. First stage consists of cyclone separators and the second stage filters finer particles. As the two stage systems only have a service interval of 400 km, Self-Cleaning Air Filtration System (SCAFS) was designed by CVRDE for this engine.
Overall, we all should agree that CVRDE, without any prior experience has done a commendable job in has designing a modern age behemoth on its own to make us less dependent on foreign countries for our needs. Also from the papers that were published, it is evident that CVRDE is also working on different engines producing different power figures for different applications ranging from 400, 600, 700 HP respectively.
The future tank will require power plants of 1500 HP or even more and as per the latest updates, the power pack is read and under testing. In 2019 GTRE did confirm that they have developed a turbocharger for the 1500 HP diesel engine and now DRDO’s Lab in monthly bulletin confirmed that “CVRDE has assembled the first prototype”. This 1500 HP engine was tested for the full output with a turbocharger, which was a developed by GTRE.
Overall interesting days ahead!