Armoured Vehicles Discussion Thread - Jan 12, 2012

[GeorgeM]

Why use multiple engines when you can do cylinder deactivation? Easier no?

Exactly. This route of multiple engines have been taken up by many companies for different applications. For some it works. Like in the refrigerated trucking industry where the truck has to run the main engine while parked to maintain freezer and a/c. Cat has a small engine now that does the refrig role. Latest proven engine tech does allow lower fuel consumption with one engine at different load cases. With 2 engines you need 2 fuel sys, cooling, nightmare of integration etc.
Honestly I feel DRDO is taking absolute baby steps in this field. My experience with Ricardo has been pathetic in the large engine field (1000-4500hp range). They have poor knowledge in lube oil sys, valve train dynamics, turbo matching etc. very minimal knowledge in system integration. They 'may be' good in auto engines field. But definitely not for large engines. AVL is a thermo-dynamics based design company. So they have good modeling of engines. They have some of the best engine 1d modeling tools in the industry. Even engineers who use Ricardo as consultant use AVL exite on the side to develop valve train and crank train. My experience says FEV is the best of the lot in large engine consultancy. But I also heard they refused to work with DRDO on this project.
In India we have very little experience in developing a large engine from 'ground up'. The DRDO spec for Arjun engine is a rather challenging one on top of that. With good consultancy we can develop one in 4-5 yrs. but you are looking at lot of foreign suppliers. Else if it is one of those develop the capability exercise then think Kaveri. Easy 10-15 yrs.

[GeorgeM]

The below comment is exclusively for large engines.
One more thing. Foreign parts will have to be there. Esp pistons, cyl head, valve seat, coated valves, hi pressure fuel system, turbo charger etc. At such hi rpm (1900) valve train is the first to fail and we dont have good valve train expertise in India. Arjun engine spec is rather challenging. Even an established tank engine company like MTU will find it difficult. This is mainly due to very high power density req. so they have to jack up the rpm to get to that power. But even with the latest tech there is a limitation on mean piston speed at ~12.5 meters per sec. (Latest Cummins QSK90 at 13 mps?) Also there are limitations on peak cyl pressure at around 230 bar. DRDO may need to go beyond on both the counts.
Also heat rejection is going to be a big issue. The best with latest friction reduction, variable valve timing etc you can get is 45% thermal efficiency max (diesel). Add a few if you can recycle the exhaust gases. Rest is lost as heat. So along with engine you need latest dev in compact heat rejection.
This is an excellent research project hence the attraction for the great scientific minds. Instead you need bunch of development engineers, service and manufacturing experts, early supplier on boarding etc. Bunch on science heads will kill this project.

[Karan M]

Apparently they want industry to drive it, not just scientists.

“Simultaneously, we have floated an Expression of Interest (EoI) to identify an Indian manufacturing partner. The consultant we select will work in a consortium with the DRDO; the army; and the Indian manufacturing partner, who will be associated with the programme from the design stage itself. We have allowed the consultants to visit manufacturing companies and report on their capability to build a modern engine,” explains Sivakumar.

The CVRDE director says the consultants will finalise the engine design within 12 months, and take 18 months more to build the first prototype. “Within 30 months, or three years maximum, the first engine would be ready for testing,” he says.

“Both Ricardo and AVL have proposed that they design and build the first prototypes. But the Indian industry will work alongside the consultant. The first design is never perfect; so the consultant will make the changes needed in design, tolerances, or materials to refine the engine. Then, in the second phase, the Indian partner will produce the engine,” says Sivakumar.

[Karan M]

That will be the biggest breakthrough, if an Indian company can make these engines by themselves and own it - including part sourcing, design etc.

[GeorgeM]

Thanks Karan. I missed to soak in the paragraphs you highlighted. That approach should help. DRDO can provide funding plus solution at a fundamental level - material science, control system, thermo-structural analysis, etc. Provide funding to a team from Kirloskar or Tata, with suppliers etc for x yrs. Tatas did a similar work with consultants for their Nano engine.
The timeline for design freeze of 12 months look a tad ambitious though. It would be prudent to take a single cylinder test engine route before design freeze. So add another 9 months.

[Singha]

what happened to the replacement 1500hp engine for Arjun mk1 that Cummins was supposed to be doing in pune with collab from CVRDE?

[vasu raya]

Eric L, if we take the MTBF as the focal point, the deactivated cylinders do not reduce that in diesel engine, a turbine easily wins on that account. The turbine loses on fuel efficiency only when subjected to variable loads while its economic in a constant run.

if we take a truck on the Golden Quadrilateral, say it maintains a average speed of 80kmph, the turbine can be run for that load, any surge can be handled by the diesel engine + charged battery bank while slump can be directed to the battery bank. The amount of time the diesel engine is engaged is reduced significantly on constant runs increasing its life. yes, the capital cost would be on the higher side, while the lifecycle costs would be reduced, an argument we use for Rafale. The import costs are high too, easily balancing the local dev cost.

In the case of the tank they mention 40:60 power needs, the lower end can be met by a turbine and all surges by a 1000hp diesel, most likely they have a efficient one with that rating already vs developing the 1500hp one.

Ultimately use of turbines may cause precision engineering to trickle down the auto industry.

[Eric Leiderman]

There are plenty of combinations available. Once you go diesel electric you can shed weight go for 2 power packs + battery pack for stealth etc. The electronics are available off the shelf used in marine and railway applications

[GeorgeM]

if we take a truck on the Golden Quadrilateral, say it maintains a average speed of 80kmph, the turbine can be run for that load, any surge can be handled by the diesel engine + charged battery bank while slump can be directed to the battery bank. The amount of time the diesel engine is engaged is reduced significantly on constant runs increasing its life. yes, the capital cost would be on the higher side, while the lifecycle costs would be reduced...

Well all that sounds great on paper but consider the following.
- Diesel engines are designed for a certain numbers of cranking(starts).
- Also every time the Diesel engine starts, the lube oil temperatures are low. As soon as the DE kicks in, it most of the time have to go straight to rated power. So DE keeps shuttling b/w zero to rated power. That will kill the bearings, pistons etc. ( low cycle fatigue, Thermal shock ).
- Also it can't have a common lube oil system b/w the 2 engines.
- You have to carry 2 different fuels etc.

In the case of the tank they mention 40:60 power needs, the lower end can be met by a turbine and all surges by a 1000hp diesel, most likely they have a efficient one with that rating already vs developing the 1500hp one

.

The 1000 hp DE will have new components to meet the more severe g-loads as well as duty cycle. Also the power density is not going to change b/w a 1500 HP and a 1000 HP as you need space for the turbine and it accessories. It will be a new engine either way.

Ultimately use of turbines may cause precision engineering to trickle down the auto industry.

I think we have very well mastered precision Engg. We have some of the best brains and suppliers in the industry in that field. This dual engine is a completely different beast compared to attempting a straight single 1500 HP DE. Not only now you have a never before attempted power dense DE now you have to integrate that with a turbine. Again very rarely attempted. Truly a different beast.

[GeorgeM]

Diesel engine acting as a generator with electric propulsion + regeneration systems? you can two small engines replacing one bigger one if needed.

If one takes a 1000 HP Diesel engine and its equivalent alternator, one will find that the alternator weighs about the same as the engine. Then you add regen system and battery packs pretty soon you have a power sys that weighs about 2 to 3 times a diesel-transmission combo.
The automotive hybrids work differently. Engine is a minor player.

[GeorgeM]

Engine concept if you really insist on dual engines.

On most modern large engines, Turbo provides about 30% of rated power. This contribution % reduces at lower powers so much so that at idling, turbo contribution is 0%. But the key is to think of Turbo Charger as a separate engine. One that shares a common combustion chamber with main reciprocating diesel engine. Some power is extracted directly at the main engine rest extracted at TC.

Now here is the trick- What if a bypass is provided such that at low power requirements, the charge air from TC bypasses the diesel combustion chamber, and instead goes through a secondary combustion chamber and powers the turbine directly. The main Diesel engine is now shut down as it receives no air. Only TC is producing power and therefore the drive axle now has to be driven directly from the TC. So a clutch arrangement is needed. You probably need a Variable Geometry Turbine. So, upto 40% of the total power requirement, only TC is providing power. For power requirements beyond 40%, the bypass opens the charge air to the main Diesel engine. Now the clutch to the TC has to be disengaged and all power comes from crank shaft alone. A good control system challenge but worth considering before jumping into the concept of integrating a separate turbine engine to a diesel engine

Additional challenge will be in the vibration mode shapes. The TC now is a bit larger and can influence engine excitations even more. One way out is NOT to mount TC directly on the engine mainframe. Have a separate mounting structure.

The difference b/w the above concept and the DRDO concept is that there is no full time gear box connecting b/w turbine and Diesel engine. So lesser weight, better integration, smaller size.
No on top of this why not make the Diesel engine a 2 stroke. But one that produces rated power at around 1100 rpm. Lower rpm means now you can go for a 2S with proper valve train like in 4S. But now you need higher boost pressure for good scavenging which you can anyhow get since you already have a slightly larger TC. You would need higher injection pressures and probably dual injectors injecting alternatively. But with a bit oversized common rail, that too can be eliminated.

Most of the issues with dual engines I mentioned in my previous posts has been addressed with this concept except for fuel. I think there may be ways around. That requires a separate post.

[vasu raya]

Sidharth, take it as armchair opinion only, this has a parallel with dual pulse motors which are state of art in t he missile arena, the booster is the DE while the sustainer is the turbine. one deviation is we don't want to switch between TC and DE as power requirement spikes above 40% but have the DE augment the TC so that combined rated power of 1500hp is acheived. Even under 40% power, step changes/surges of power are effected by DE for fuel efficiency sake, the TC increments power as well just not under load and then maintains the new power level disengaging the DE.

As for fuel google says turbines have been run on Bunker C or even ethanol

regarding battery pack there is electric reactive armor where the ERA bricks are essentially capacitors and probably can double as the battery pack

if one wants to go diesel electric, wonder how the electric motors fare while the tank is fording

[GeorgeM]

...one deviation is we don't want to switch between TC and DE as power requirement spikes above 40% but have the DE augment the TC so that combined rated power of 1500hp is acheived.

Thank you Vasu Raya. Yes that is exactly how it works, but I guess my long winded description might have convoluted it. Above 40% power requirement it works as a pure turbo charged 2 stroke diesel engine.

Even under 40% power, step changes/surges of power are effected by DE for fuel efficiency sake, the TC increments power as well just not under load and then maintains the new power level disengaging the DE.

Yes that sounds good improvement

As for fuel google says turbines have been run on Bunker C or even ethanol

Regarding fuel. Here is what I found on wiki - Link on fuels
"Gas turbines accept most commercial fuels, such as petrol, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85, biodiesel and biogas. However, when running on kerosene or diesel, starting sometimes requires the assistance of a more volatile product such as propane gas"

if one wants to go diesel electric, wonder how the electric motors fare while the tank is fording

I guess permanent magnet motors may be feasible. Idea is to keep the current to the stator only. But permanent magnet moors tend to have less capability compared to armatured ones.

[vic]

IIRC DRDO is targeting 90% of technological level of MTU 883 in their Bharat Power pack using foreign consultants and all major components outsourced or imported. The two engine thingie is just loud thinking about possible course of action in the future.

[vasu raya]

On the topic of ignition,

Researchers put spark into scramjets

Instead O'Byrne and PhD student Stefan Brieschenk, have focused a high-powered laser on the fuel jet, which creates a precise spark in the hydrogen fuel.

It does this through a phenomenon known as cascade ionisation, which occurs when the high-intensity beam literally "rips electrons off" the hydrogen molecule, creating a plasma that is the "spark".

The spark has peak temperatures approaching 100,000°C, compared with a conventional electrical spark of a few thousand degrees Celsius. At this temperature the hydrogen molecules are torn apart and they become highly reactive and accelerate the reaction between the fuel and air.

The researchers proved the concept in a hypersonic wind tunnel by creating conditions where hydrogen would not burn, and then using this approach to ignite it.

Importantly, says O'Byrne, because each laser pulse lasts for a few nanoseconds it requires less energy than a continuous electrical spark.

He says the laser-ignition may also have applications in generating greener energy through improved ignition of gas-fired engines for power generation.

[Gurneesh]

Engine concept if you really insist on dual engines.

On most modern large engines, Turbo provides about 30% of rated power. This contribution % reduces at lower powers so much so that at idling, turbo contribution is 0%. But the key is to think of Turbo Charger as a separate engine. One that shares a common combustion chamber with main reciprocating diesel engine. Some power is extracted directly at the main engine rest extracted at TC.

Additional challenge will be in the vibration mode shapes. The TC now is a bit larger and can influence engine excitations even more. One way out is NOT to mount TC directly on the engine mainframe. Have a separate mounting structure.

Turbocharger does not provide 30% hp by itself; it actually helps the engine produce more power by cramming more air into the engine cylinder. More air in the cylinder requires more fuel and that is what increases the hp.

Using a typical sized turbocharger, in a turbo-shaft configuration, to extract shaft hp will not give any significant horsepower if any. To get any meaningful hp, the turbo will have to be much larger in size; to put things in perspective, the turbo-shaft engine of PC7 produces 500 shp and it has 4 compressor stages and two turbine stages!

Another factor to be considered is that the turbocharger needs to be good at it's first job, i.e., turbocharging the diesel engine and that puts a limitation on how big or small the turbo can be. The turbo will max out too soon and starve the engine if it is too small; on the other hand, the engine will not be able to generate enough flow rate to spool the turbo if the turbo is too big and there will be no turbocharging.

On the topic of ignition,
Researchers put spark into scramjets

Actually, this is a fairly common practice in labs doing gas turbine/IC engine research; especially, the labs that use laser diagnostics. All one needs is a high power Nd-YAG laser (which almost any lab doing laser diagnostics has at hand). Must say though that this beats the spark plugs all day as with lasers the precise location of the ignition source can be controlled and also the avenues for optical access increase and the spark plug is no longer there.

[ArmenT]

Engine concept if you really insist on dual engines.

On most modern large engines, Turbo provides about 30% of rated power. This contribution % reduces at lower powers so much so that at idling, turbo contribution is 0%. But the key is to think of Turbo Charger as a separate engine. One that shares a common combustion chamber with main reciprocating diesel engine. Some power is extracted directly at the main engine rest extracted at TC.

Additional challenge will be in the vibration mode shapes. The TC now is a bit larger and can influence engine excitations even more. One way out is NOT to mount TC directly on the engine mainframe. Have a separate mounting structure.

Turbocharger does not provide 30% hp by itself; it actually helps the engine produce more power by cramming more air into the engine cylinder. More air in the cylinder requires more fuel and that is what increases the hp.

Kinda close. Basic concept is that the more fuel you burn in the cylinders = more power. However, with a normally aspirated engine, you can only put X amount of fuel in a cylinder per cycle, because there is only so much oxygen in the air. If you add more fuel than that, the extra fuel will not get burned in the cylinder because of lack of oxygen and the wasted unburnt fuel comes out of the exhaust. This puts a top limit on how much power you can generate for a certain engine volume.

Clearly, if we need to extract more power (i.e. burn more fuel), we need to somehow ensure that more air (or specifically, more oxygen) gets into the cylinder, so that we can completely burn more fuel. There are a few ways to do this. One way is to compress the air before it goes into the cylinder, thereby packing more air into a cylinder than a normally aspirated engine gets. This is accomplished by attaching a turbocharger or a supercharger to the engine intake. Another way is to supply oxygen from a separate source (e.g. a nitrous oxide supply system), but that can only supply extra oxygen for a short while and we won't go into that here.

[GeorgeM]

Turbocharger does not provide 30% hp by itself; it actually helps the engine produce more power by cramming more air into the engine cylinder. More air in the cylinder requires more fuel and that is what increases the hp.

I guess the fundamentals are well understood in this discussion. If you take a Qsk60 or a 3512 engine and remove the tc, you will get approx 30% less rated power. The suggestion was to think of it as 2 engines only to help understand the concept.

Using a typical sized turbocharger, in a turbo-shaft configuration, to extract shaft hp will not give any significant horsepower if any. To get any meaningful hp, the turbo will have to be much larger in size; to put things in perspective, the turbo-shaft engine of PC7 produces 500 shp and it has 4 compressor stages and two turbine stages!

This comparison helps. So I guess then this dual engine turns out to be even more difficult. Just good only for some paper talk may be.

Another factor to be considered is that the turbocharger needs to be good at it's first job, i.e., turbocharging the diesel engine and that puts a limitation on how big or small the turbo can be. The turbo will max out too soon and starve the engine if it is too small; on the other hand, the engine will not be able to generate enough flow rate to spool the turbo if the turbo is too big and there will be no turbocharging.

that is why the proposed concept had a VGT. But looking at the previous para on turbo-shaft PC7, this dual engine concept may not cut it after all. Or have the TC supply power only during idling. But either way I have my reservations and have summarized my feeling in the last para below

At the end I strongly believe that DRDO should pursue a single engine concept. It will take 4 yrs to productionize the engine. Then it would need to be put on a few Arjuns and field proven or battle hardened for 1 more yr. if you start on Jan 2014, you can have proven engine in 2019 Jan.

[Sagar G]

Relax guys don't lose sleep over this dual engine concept since

Even as CVRDE develops this technological capacity, it is looking further ahead at a hybrid engine for the FMBT after 2030. Sivakumar says that a tank remains static for at least 40 per cent of the time in battle, during which time its engine idles. “This means that 40 per cent of the time, you wastefully run a 1,500 Hp engine, guzzling diesel and giving away the tank’s position, while you need very little power for running electricals like the radios and gun control equipment or for moving the tank slowly. So, we are evolving a hybrid technology concept in which the tank will have two engines: a 500 Hp engine for low power mode and another 1,000 Hp engine that kicks in when high power is required, e.g. for manoeuvring in battle,” explains the CVRDE director.

It's just an evolving concept to be worked upon well into the future, for now it's the 1500/1800 HP single engine onlee.

[vasu raya]

On the contrary, they should do research with spinoffs in the civilian sector, this can be done as long as the goal of substituting import of engines for the heavy segment is met, Arjun's engine is just a small part of it. The RoI would be there regardless of the whims and fancies of a single customer.

[Eric Leiderman]

Sidharth
The turbo as a low power pack is a superb concept. Yes the turbo charger and/or turbo generator will be comparatively inefficient due to having to having to cater to such varying needs , but a turbo does not weigh much, It could be permenantly coupled to a alternator (variable speed) and you have a hybrid concept built in.
A two stroke diesel is light but the stroke(ideally) will have to be longer for scavenging and you may not have the space for that.

[vasu raya]

The turbine + piston engine concept was worked in the 1950s, the turboshaft/prop completely took over in the case of aircraft

Napier_Nomad

Gas_turbine#Tanks

The French Leclerc MBT's diesel powerplant features the "Hyperbar" hybrid supercharging system, where the engine's turbocharger is completely replaced with a small gas turbine which also works as an assisted diesel exhaust turbocharger, enabling engine RPM-independent boost level control and a higher peak boost pressure to be reached (than with ordinary turbochargers). This system allows a smaller displacement and lighter engine to be used as the tank's powerplant and effectively removes turbo lag. This special gas turbine/turbocharger can also work independently from the main engine as an ordinary APU.

whether we can push such APU to address the 40% load is a question.

[vic]

Tender issued for developing tank engine

https://www.google.co.in/url?sa=t&rct=j ... 7178,d.bmk

[Pratyush]

have been reading the issue of the 2 engine setup for the future tank. Reading what is posted on the thread. It seems that hyperbar is planned. as the basic requirement is identical.

[vasu raya]

turbocharging is said to contribute 30% of the rated power, wonder how high Hyperbar would take it to, basically a 1000hp rated DE would be replaced with a much smaller one assuming 500hp is provided by a turboshaft driven APU, in the process they might indigenize the PC7 engine. And corresponding to the gears in the 40% load regime, multiple power settings for the APU can be fixed, in addition a heat exchanger for cycling warm lube in the DE can be added.

if the Hyperbar takes off, the current Kaveri in a turboshaft configuration can be run in a combined cycle with multiple diesel engines in locomotives. Its compressor running air through as many cylinders.

Hopefully they got the engine block casting technology, a pre-requisite for Hyperbar?

[GeorgeM]

have been reading the issue of the 2 engine setup for the future tank. Reading what is posted on the thread. It seems that hyperbar is planned. as the basic requirement is identical.

I think the hyperbar engine is a bit different. See the line below

where the engine's turbocharger is completely replaced with a small gas turbine which also works as an assisted diesel exhaust turbocharger, enabling engine RPM-independent boost level control and a higher peak boost pressure to be reached (than with ordinary turbochargers)

I think in Hyperbar they have a full time, independent turbine engine. Seems like some of the compressed air from the gas turbine is bled into the main diesel engine. Hence the comment "rpm independent boost control". In the dual engine concept we have been discussing, the turbine is not independent. Above 30 or 40% power all charge air is fed into the Diesel engine.
Hyperbar does offer some advantages, but current technology allows only upto 230-240 bar anyways. Once you go above that, engines will have significantly shorter overhaul intervals. Also weight goes up. Gasket leak is another issue. Cyl head casting cooling have to be very tightly control thru out the core. So considering all these, I don't see much advantage when they say "... higher peak boost pressure to be reached". Potential is there that is it.
Either methods I think we can have a compact engine.

[vasu raya]

Frech Lecerc is in service, so Hyperbar is not a 'potential' thing.

[Gurneesh]

The turbine + piston engine concept was worked in the 1950s, the turboshaft/prop completely took over in the case of aircraft
.....
whether we can push such APU to address the 40% load is a question.

According to wiki, the Leclerc uses a Turbomeca tm 307b APU for it's hyperbar system. Your article also mentions that the gas turbine acts as an APU when the tank is stationary and thus, allows the diesel engine to shut off. Even a 30 kW APU is only around 40 hp. Again, for the APU to give out 500 hp, a bigger gas-turbine engine is needed. Another thing to note is that at low to no loads the efficiency of gas turbines suffers a lot; therefore, 500 hp APU running to give only around 13 hp (10 kW which IIRC is the Arjun Mk2 APU) will also have very bad efficiency. In that respect, the hyperbar system is good as the boosting and APU responsibilities are given to a gas turbine while the Diesel engine is solely responsible for motion.

I think in Hyperbar they have a full time, independent turbine engine. Seems like some of the compressed air from the gas turbine is bled into the main diesel engine. Hence the comment "rpm independent boost control". In the dual engine concept we have been discussing, the turbine is not independent. Above 30 or 40% power all charge air is fed into the Diesel engine.
Hyperbar does offer some advantages, but current technology allows only upto 230-240 bar anyways. Once you go above that, engines will have significantly shorter overhaul intervals. Also weight goes up. Gasket leak is another issue. Cyl head casting cooling have to be very tightly control thru out the core. So considering all these, I don't see much advantage when they say "... higher peak boost pressure to be reached". Potential is there that is it.
Either methods I think we can have a compact engine.

You will need some engine to take 230 bar of boost pressure!

Typically, for heavy duty diesel engines the boost pressure is below 5 bar. As per wiki, the boost pressure for the hyperbar system is 7.5 bar.

Actually, hyperbar accomplishes the same purpose as a supercharger. At low engine RPM, in hyperbar the APU is fed extra fuel to boost the engine; a supercharger, on the other hand, takes power from the engine crankshaft. This eliminates the turbo-lag that most turbos suffer from. The hyperbar also has an added benefit of being able to operate as an APU, while, the supercharger has the benefits of being less expensive and simpler to implement.

Another thing that people should take into account is that the gas turbines are much more vulnerable to damage due to dust than a conventional diesel engine.

[vasu raya]

Gurneesh, we see the experience of using gas turbine in M1 Abrams, principal issues being fuel efficiency while idling and dust intake while operating in deserts. With the 2 engine concept, idling inefficiency of a 0-500hp VGT/APU is not as bad as a 0-1800hp turbine, being VGT maybe multiple power settings are possible with its lowest setting, it can be close to the current APU.

On the plus side,
40% of the time the DE is not engaged improving MTBF
and when the DE is the prime mover you got Hyperbar operation, the APU can also work as a swift sidekick

Americans have managed to add filters to protect the turbine, it is as much a problem with Dhruv or Apache when flying low.

[Gurneesh]

Gurneesh, we see the experience of using gas turbine in M1 Abrams, principal issues being fuel efficiency while idling and dust intake while operating in deserts. With the 2 engine concept, idling inefficiency of a 0-500hp VGT/APU is not as bad as a 0-1800hp turbine, being VGT maybe multiple power settings are possible with its lowest setting, it can be close to the current APU.

On the plus side,
40% of the time the DE is not engaged improving MTBF
and when the DE is the prime mover you got Hyperbar operation, the APU can also work as a swift sidekick

Americans have managed to add filters to protect the turbine, it is as much a problem with Dhruv or Apache when flying low.

It is a misconception that gas turbines are inherently more efficient than diesel engines. Gas turbines only become more efficient when the waste exhaust is used to produce steam in what is called as a combined cycle. Another point to note is that smaller the gas turbine, lower the efficiency. Other disadvantages of gas turbines include lower mtbf, high susceptibility to foreign particles and sharp fall off in efficiency when operated outside of optimum limits. And running a small 500 hp GT at < 50 hp (<10% max load) will make an already inefficient turbine more inefficient.

The only advantage gas turbines have over diesel engines is the power to weight ratio and perhaps the capability to produce very high power (> 50 MW). The power to weight ratio makes a lot of difference in aircraft (enough to negate the lower efficiency) but not so much in a 50 ton tank.

Check out the figure 2 in this pdf
http://www.man-gasturbine.com/files/new ... rbines.pdf

Another source
http://www.wartsila.com/en/reciprocatin ... efficiency


Coming to VGT (which means Variable geometry turbine), I have only seen that applied to turbochargers and havn't seen one incorporated into gas turbine. And even VGT does not cure the turbo lag completely.

[GeorgeM]

Frech Lecerc is in service, so Hyperbar is not a 'potential' thing.

I meant 'potential' for higher in cylinder pressures in future when the technology allows disel engines to handle higher cylinder pressures.

[GeorgeM]

You will need some engine to take 230 bar of boost pressure!
Typically, for heavy duty diesel engines the boost pressure is below 5 bar. As per wiki, the boost pressure for the hyperbar system is 7.5 bar.

230 bar of peak cylinder pressure NOT boost pressure. Read my comment and you will see that I am talking about cylinder casting failures not manifold casting issues.

[vasu raya]

ok Gurneesh, why aren't combined cycle gas turbine - CCGT not operated in land mobile platforms? the coolant/steam in the second turbine will be part of a closed turbine like water in a radiator

used this as ref:
Introduction to Gas Turbines

In the 2 engine concept, with a CCGT and a Diesel engine, the cruise mode which is part load for a 1500hp power pack can be taken over by the CCGT driven genset operating at its rated power, in reality when operating in the upper band of >65% load, the efficiency variance of the CCGT is not more than 5% so it can sustain multiple gear box speeds with loads in that band.

when needed and at the expense of fuel efficiency, the GT gives better acceleration to the tank working in tandem with the DE

Then there is Hyperbar with a potential of greater than 7.5bar, its current difference with 5bar from a turbocharger doesn't seem much

[Gurneesh]

230 bar of peak cylinder pressure NOT boost pressure. Read my comment and you will see that I am talking about cylinder casting failures not manifold casting issues.

OK, was not apparent from your earlier post. BTW, too high a boost pressure will also cause issues in the engine cylinder much earlier than it causes any failures in the manifold casting. Generally, the head gasket is the first one to give up.

ok Gurneesh, why aren't combined cycle gas turbine - CCGT not operated in land mobile platforms? the coolant/steam in the second turbine will be part of a closed turbine like water in a radiator
...
In the 2 engine concept, with a CCGT and a Diesel engine, the cruise mode which is part load for a 1500hp power pack can be taken over by the CCGT driven genset operating at its rated power, in reality when operating in the upper band of >65% load, the efficiency variance of the CCGT is not more than 5% so it can sustain multiple gear box speeds with loads in that band.

when needed and at the expense of fuel efficiency, the GT gives better acceleration to the tank working in tandem with the DE

Then there is Hyperbar with a potential of greater than 7.5bar, its current difference with 5bar from a turbocharger doesn't seem much

I am not sure why CCGT are not used in land mobile platforms, but I think it still has to do with efficiency as gas turbines become favorably efficient (even with CCGT) only after a certain power range. Another factor is practicality of having a GT in the vehicle as well as drive-ability of the resulting platform. IIRC GT's are sluggish and have issues with transient response.

Actaully 7.5 bar with hyperbar is 50 % higher than the 5 bar!

Doing some digging on the hyper bar engine led me to this discussion:
http://z4.invisionfree.com/NSDraftroom/ ... topic=8344
Look for the post of Sumer, where he says that hyperbar engine can take the higher boost pressure as the engine is in an opposed piston configuration as shown below:


Parts of his post (FWIW)..

As for fuel consumption. Hyperbar's change it. The gas turbine has to have fuel, but since it's not loaded it doesn't eat as much, and since it's size does not need to scale with the engine to gain appropriate boost, it's fuel consumption does not really go up when the engine's size goes up.

The LeClerc fuel consumption is around 2.8L/km in terms of travel. Which puts it far ahead of either the M1 or T-80's gas turbines (Both in the ~4.5L/km range), and ahead of any new gas turbine developments (Still over 3). It's not good compared to, say, a 30+ year old duesel (MTU-883 is 2.2L/km in a Leopard 2A6), or newer ones (~2L/km is expected of any next gen tank, for example the K-2 and Type 10).

You need serious cooling, which (Much like pure GT tanks) takes up a lot of space. Hyperbar engines eat lost of air, and shit out lots of air. So you need to have a lot of venting. A lot of it. But better cooling is always a plus, especially in hot climates. So I am kinda biased in that regard. I have a really complex system (Besides the weird Crower cycle) for the MCA-7's engine. And the M's new engine will be even weirder.

Lastly, in terms of volume. Consider the 6TD-2, from Ukraine. It's 16.3L, 1200hp, non-charged. That's ~73hp/L natural. Two things help this, it's two stroke (So it has a 1/2 power stroke not a 1/4), and it runs higher compression. Slapping a dedicated hyperbar system to it is likely to net you ~2000hp.

Another discussion here:
http://www.tank-net.com/forums/index.ph ... opic=35077

[Singha]

while I cannot claim to understand most of the stuff above, what is the realistic exec summary of a engine that can be used in 2018 given our domestic level and prospects of foreign collab? has the leclerc engine proved reliable and combat-ready in gulf arab use - UAE has 388 of these tanks....are they placed nicely for show in hangers or regularly work up in the field in adverse conditions ? Leclerc is one tank that has no combat use in the gulf so far.

are we stuck with a 1500hp single engine + APU (for AC and electro-optics) or this dual engine thing has promise of delivery in 6 yrs?

[abhik]

while I cannot claim to understand most of the stuff above, what is the realistic exec summary of a engine that can be used in 2018 given our domestic level and prospects of foreign collab? has the leclerc engine proved reliable and combat-ready in gulf arab use - UAE has 388 of these tanks....are they placed nicely for show in hangers or regularly work up in the field in adverse conditions ? Leclerc is one tank that has no combat use in the gulf so far.

The UAE tanks are powered by MTU MT883 engines, not the fancy French engine. Its displaces 27 liter and produces 1500+ hp in various versions. Those specs are what DRDO seems to be trying to match with their own engine. Considering that the MT883 itself is almost 2 decades old, no reason we shouldn't be able to do it, especially with foreign consultants and local industry involved.

[GeorgeM]

while I cannot claim to understand most of the stuff above, what is the realistic exec summary of a engine that can be used in 2018 given our domestic level and prospects of foreign collab? ...
are we stuck with a 1500hp single engine + APU (for AC and electro-optics) or this dual engine thing has promise of delivery in 6 yrs?

Disclaimer- this is purely my take based on a) interaction with engineers in engine field within India. b) interaction with engine component suppliers within India.

Path 1 - as pandyan mentioned, localizing an MTU engine has the least new technology introduction. I believe there is enough manufacturing capability in-country to do this. Where it is not available, we have the capability to absorb. But why would MTU localise for a few thousand engines?
Path 2 - develop a new Diesel engine. We need foreign consultancy help here. So give the work to OEMs like Kirloskar, Mahindra etc as DRDO tend to attract technology embargo. Govt can fund xx% of the project. OEMs can develop variants ( power gen, marine, V16, V20 etc ) later from the base engine. But again the question is why would any Indian OEM develop a new engine in this category which has some very well entrenched strong competition. Also this large engine field is getting saturated and on top we now have new engines coming from MAN, Chinese CNPC, Hyundai etc. These new in-development engines are much more compact and have improved technology over the older kings of the hill- Cat, MTU & Cummins. They are also expected to give better fuel numbers and are built ground up ready for dual fuel usage, which is expected to be the next big thing in large engine field(shale gas driven change).
Path 3 - Get an Indian OEM to buy a good engine company that already has a good market/brand value, similar to how TATAs bought JLR. MTU was up for sale a few yrs ago that too cheap. Buying other engine co, you may not get a compact power dense tank engine but atleast we can quickly develop one. MTU was a fantastic option as they also own l'orange, one of the few remaining hi pressure fuel system companies. Bosch has the lions share then rest by l'orange, denso etc. You need hi pressure fuel sys technology which is nearly impossible to develop on your own.

Having presented the 3 options, systems like Turbo, hi pcp pistons, dozens of different sensors, metallic coating (stellite etc) are also very very difficult to develop. So I don't think we can ever achieve a 100% Indian engine.

You may have also noted that the dual engine path is even more difficult. So for a 2018 timeframe, a single engine along path 3 is the best option followed by path 2. But DRDO it seems to me is proceeding along path 2 as the primary option for a good sound reason.

[Eric Leiderman]

Sidharth

No Indian Manafacturer will put in money for R & D without a firm order on the horizon if certain paameters are met.

so 1) Army has to set its parameters down as to what it wants. How many it wants, when it wants
2) Even if GOI is putting up 80% of R & D seed money unless firm order is available on
completion of project Indian manafacturers will be hesitant. Look at the artillary saga
3) Ideally GOI should put seed money into Educational institutes, which should be mentored
by private industry, There have to be multiple projects with possible civilian spinoffs.
Even if a percentage of hese frutify the base has been laid. If the power plant in not
available in a few years we can fall back on MTU Renk , Go the Kaveri route, though this
project has a better chance of seeing dalight. Another project is the engines for a medium
powered rotary wing that should be less daunting than the power plant for a small fighter
jet.


Over time many of these concepts hae been brought up on this very forum, hopefully 10 years down the line we will not be discussing the same issue.

[vasu raya]

Gurneesh, GT being sluggish goes aganist the very grain of Abraams tank design isn't it? after the compromise on fuel consumption

btw, DRDO developed a 55hp wankel engine for Nishant, and Abrams uses a wankel engine based APU, whether such an non-GT APU is sufficient for Hyperbar operation as well is another question

With DE as the prime mover and the above APU, there is no idling load on the CCGT and the CCGT efficiency starts at 65% load which is 500hp * .65 = 325hp

Both CCGT driven genset and a diesel electric drive feed the electric propulsion reducing the transmission complexity

Additional cooling requirement gives the opportunity of heat scavenging by the steam turbine.

One nice day they may decide to operate the Arjun in Tibet, the GT provides cold start option.

-----------------

On the executive side, while setting a reachable goal is good, by the time DRDO reaches there say in 5 years, the competitors would bring new designs into market and offer them to us, and the DRDO's lone customer gets tempted to get those, they change the requirements citing obsolescence of the DRDO's engine, a political circus starts and DRDO gets accused of re-inventing the wheel.

Since we don't have a local diesel engine in the first place its ok to be conservative for the first iteration at the same time they should open the risk profile so that another parallel effort can be productionized at say 7 years, one more at 10 years, yes it doesn't square with bean counting policies and puny R&D budgets.

Another way is sharing R&D, there are many companies interested in the heavy diesels, CVRDE, IN, BEML and Railways each can work on a different design. Each market will have this load to non-load ratio differences needing different design optimizations.

[vasu raya]

posting it here due to mention of engine concepts,

Diesel-Electric Helo Work Going Under Cover?

Having talked publicly about its research into diesel- and hybrid-electric-powered light helicopters, Eurocopter has become coy as those plans get closer to reality.

The EADS company has two programs under way: BlueCopter to replace the single turboshaft in its EC120 with a diesel; and EADS Innovation Works' eCO2avia to develop a hybrid diesel-electric propulsion system.

Asked at this week's Heli-Expo show about progress with the hybrid-electric concept, CEO Lutz Bertlng said Eurocopter "is actively working on it", but would not say more because it was competively sensitive. Hmmm.

As previously described, the eCO2avia has electrically driven main and tail rotors powered from four sources: two battery packs plus generators on two diesel engines. Batteries and engines power the helicopter for take off; engines power the cruise and recharge the batteries; and batteries alone are used for a quiet, clean landing,

As for the diesel, Bertling says he expects the slow-selling EC120 "to have a second life with diesel power, because it will become dramatically cheaper." A diesel will still burn jet fuel, but far more economically than a turbine. He says Eurocopter has selected a powerplant - it's a non-aviation diesel so needs to be certificated. A diesel-powered EC120 will not be available until after 2012-2013, he says, because Eurocopter has other priorities.

BlueCopter and eCO2avia will share diesel technology, Bertling says. EADS has previously expressed interest in EcoMotors OPOC opposed-piston, opposed-cylinder engine. EcoMotors says the OPOC is 30% lighter, a quarter the size and 50% more fuel-efficient than a conventional modern turbo-diesel.

land lubbers have the option of CCGT with higher efficiency and the OPOC sounds close to the HyperBar configuration except for being lighter and fuel-efficient than a turbo