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Article:
The Kaveri Saga
Kaveri also has a shortfall of around 12%, and it has produced 70-75 kN throughout its development. There are a total of 10 versions of Kaveri: from K1 to K9, K9+, or K9*. Kaveri was started with an ambitious weight target of 1000 kg. Later revised to 1100 kg for LCA and again revised to 1050 kg. The first Kaveri engine (K1) weighed 1423.78 kg. GTRE undertook weight reduction exercise starting in 1993, and the weight of K9 was 1235 kg and finally the K9+, which is 1180 kg. To further reduce the weight, the use of blisks (bladed disks), PMC ducts, which weigh 26 kg compared to metallic 32 kg, and powder metallurgy disks, which will require a high-pressure isothermal press that India does not possess as of now, we do have a 2000 MT ton isothermal forge at MIDHANI, which was used to make disks for all five stages of the high-pressure compressor of andour engines, which power the Jaguar aircrafts of the IAF. The aim of Kaveri has achieved a thrust-to-weight ratio of 6.5 against the target of 8.
The thrust and weight shortfalls are just the tip of the iceberg; Kaveri also had a fair share of other problems:
- U Certain critical and crucial activities for successful development of Kaveri, viz. development of Compressor, Turbine and Engine Control System, have been lagging behind despite increase in cost by Rs 186.61 crore - CAG Report No. 16 of 2010
- GTRE has been unable to freeze the design of the turbine blades, the compressor has witnessed mechanical failure in performance and the engine control system is not flight-worthy. - CAG Report No. 16 of 2010
- The Kaveri engine which is designed to meet the conditions of operating fighters in the Indian environment is perhaps technologically more challenging than the airframe.
The Core Engine demonstration, which was planned for 1990, happened in 1995; Full Engine was demonstrated in 1995 instead of the planned 1992. The historical circumstances and geopolitics didn't help the program either. The LCA was to use Kaveri in the production variant while using Electric F404-GE-F2J3. In 1995, the US approved the sale of the 404 engine to India, and eleven of them were purchased to be fitted in early demonstrators of the LCA.
In 1998, after the Pokhran Tests, the US sanctioned India, all support was withdrawn, and the LCA's last hope was the Kaveri engine. In 2001, LSP-1 made its first flight at Mach 2.1 powered with an F404-F2J3. The US sanctions were lifted, and Tejas went into production with F404-IN20 engines.
The main issues with Kaveri engines were blade flutter, screeching noise, and
afterburner oscillations. There were also problems with the low-pressure compressor, which is why the entire frontal section was redesigned for KDE. The problem with the fan was that of efficiency surge margin and flutter; for HPC, it was blade high-cycle fatigue failure and shortfall of performance compared to what was expected. For combustors it was pressure loss, pattern factor, and structural integrity; for afterburners it was screech, thrust boost, and buckling. At the time of writing this article, all the problems are mostly solved. The issue with afterburner instability was with the fuel spray nozzles, and mostly the afterburner was stretched.
There was also an issue of flickering, which was solved back in 2010. Another issue is the very low bypass ratio, which leaves less air for cooling. The in-house blades used by GTRE initially failed; this led GTRE to procure disks, blades, and control systems from Snecma. The major issues with Kaveri as of today are resolved. Safran did an audit on the engine a couple of times; they noticed some problems with the afterburner, and they were resolved.
13 engines are made till 2021, including 9 full prototypes (K1 to K9) and 4 core engines, all upgraded to the K9+ standard.
Two of the six Kaveri engines made in 1998 went for testing in Russia at CIMA, and a series of tests over two years were to examine its ability to withstand low pressure and temperature at high altitudes. Later in 2004, Kaveri failed high altitude testing in Russia. By 2008 Kaveri underwent 1,700 hours of ground testing in India and was sent to Russia twice. In 2011-12, Kaveri was tested in Russia by replacing one of the four engines of the Il-76 at a maximum altitude of 12 km and a forward speed of 0.7 Mach.
After conducting thorough engine ground runs, the scientists successfully completed the taxi trials and the maiden flight test of the Kaveri engine with the IL-76 aircraft on November 3rd, 2011, followed by three additional flight tests. The engine was again successfully tested in 2012 at an altitude of 6000 ft at Mach 0.6 speed for 55 hours in Russia. During this testing, Kaveri was able to achieve 49.2 kN dry thrust against a 51 kN target and 70.4 kN wet thrust against 81 kN.
In 2012, it was confirmed that a version of Kaveri (K9+) with its afterburner removed, called the Kaveri Derivative Engine (KDE), will be used to power the Indian Unmanned Strike Air Vehicle, or AURA, what is now called the Ghatak UCAV.
During this time there was also a proposal to invite a foreign engine house to solve the problems with the Kaveri engine called K10. This was in discussion since 2008 but was never approached. In 2014 France proposed investing 1 billion euros as part of the Dassault Rafale offsets deal and suggested a joint venture with DRDO to swiftly revive the Kaveri engine program and make it airworthy by 2018. Everyone was fine with it; it required them to do nothing. Later, France offered the M88 core to be used, and this venture fell apart.
Kaveri was using DS blades in the LPT and HPT section, but the KDE is using CMSX4 for HPT blades, as revealed in an interview by Dr. S.V. Ramana Murthy (GTRE Director), who also recommended India to set up its own strategic materials reserve to store or bank critical materials that India will require for making these engines. He also talked about CMSX4 blades being made in India but raw materials still being imported.
We have also developed a TBC coating unit with ARCI, Hyderabad, and DMRL for yttria-stabilized zirconia coating. The project is more or less in research mode and has not been used for production yet. The SX blades in KDE does use TBC coating, but it is applied by some other machine. ARCI has also developed 150 kW Axial Suspension Plasma Spray, an alternative method for TBC. GTRE is also using EDM machines from Makino for cooling holes.
Talking about single-crystal blades, the HAL makes single-crystal blades for AL31FP engines, which power the Su-30MKI of the IAF, using the Bridgman–Stockbarger technique. The AL31 engine is 53% by cost indigenous and 87% of the components. One can imagine the disks and raw materials are still being imported. A contract was signed with HAL to make 240 AL31FP engines to overhaul Su-30s. The indigenous content will climb to 63% and average 54%.
DMRL has also developed their own single-crystal blades, like DMS4 with intricate cooling channels. The DMS4 is officially a 3rd Gen SX alloy, although there exists an argument that DMS4 is a 4th gen alloy; we will stick to the official definition given in papers published by DMRL. DMS4 is in the same league as CMSX10, Rene N6, and TMS75. DMS4 offers 1140°C TET compared to 1104°C of Rene N6. DMS4 is also patented. It also has a metal temperate capability of 1140°C against 1135°C of CMSX10, 1110°C of TMS 75 and 1150°C of TMS 196 (5th gen alloy) used in XF5(49 kN Japanese engine). Also, one can imagine the TET you can achieve with proper use of DMS4 from its heat treatment. The details about DMS4 show that it lies in the same league as some of the alloys.
Info about DMS4 from:
There is also DMD4, a directionally solidified alloy derived from DMS4. Developed as a columnar grain superalloy for cost-effective turbine airfoil parts. Solutionized between 1300°C and 1330°C over 30 hours.
Now the question is why aren’t we using DMS4 if we have it? I think it was because the goal was never the performance; Kaveri already had a lot of trouble back in 2010, and they were dealing with it, and on top of it, introducing an untested, new material in the engine would have complicated their already very complicated problems. Since they have chosen tried and tested CMSX4, a second-generation alloy to be used in HPT of KDE. The Kabini was using Supercast 247A; maybe that's been replaced with the superior DMD4 alloy. Kaveri was also using Superni 718A for HPC. MIDHANI has also developed the Superni-115 LPT blade blank, although it can't be confirmed if Kaveri is using it or not.
DMRL has also made low-pressure turbine blisks for STFE engines. DMRL has also worked on serpentine air cooling for SX blades.
The first KDE was delivered to GTRE in late 2024, soon followed by a second prototype, with both undergoing high-altitude testing in Russia. Where they have more or less achieved their goals. According to a report by ET, on Dec 24, 2024, after completing its high-altitude testing, the engine is ready for real-world evaluation on a flying test bed.
There is another simultaneous project going on where a redesigned afterburner is being made by BrahMos Aerospace, who won the tender in 2020 from GTRE. The AB will then be integrated with KDE and will probably be used on a dual-engine aircraft or LSP Tejas for certification and demonstration purposes.
Today, India has all the building blocks to make its own 4th-gen engine with many PSUs and private players being the first-tier suppliers for global OEMs. A lot of work is being done on composite materials to sustain temperatures as high as 2000°C. Other than GTRE, there is also the Aero Engine Research and Design Center (AERDC) of HAL's engine R&D wing, which has developed the HTFE-25 and HTSE-1200 engines, although the technology is a generation older than what is used in Kaveri. Then there is also MIDHANI, which has developed a wide range of materials since the program began, including materials like
Inconel 718.
The majority of problems can be solved, and India can have its own engine with adequate manufacturing and testing infrastructure. But to be optimistic, HAL is setting up a national facility with a 50,000-ton die forge press and a 20,000-ton isothermal press. For many uses, the facility will also make titanium bulkheads for AMCA. The 20,000-ton iso press will be used to make powder metallurgy disks. Then India will need to use blisk for weight reduction of the engine. and use of composite materials in the AB.
Then there is the joint venture deal with foreign OEMs to make a 110 kN engine, which will replace GE F414-IN6 in the future, the front runners of this deal being Rolls-Royce and Safran. Both are offering everything India lacks more or less, and the deal basically includes GTRE getting know-how and know-why, a flying test bed, and other manufacturing and testing infrastructure required to make this engine. The development of this engine will take 10-15 years and will require funding of $4-6 billion USD.
