Gasoline vs. Diesel Turbo longevity

[younglearner]

I was wondering why it seems that a cummins turbodiesel can go around 400,000 miles before it's first overhaul but gasoline turbocharged engines in some cases have problems doing having that before their turbos experience some sort of failure?

 

[Retracnic]

I think the answer has to do more with design criteria than it does with specific differences between diesel and gasoline engine operation. Simply put, the typical diesel engine (and it's subcomponents) are designed and built to last longer than it's gasoline counterpart.

Assuming, for the sake of discussion, that both are "built to last", then we can take into account some operational concerns. The typical diesel engine sees more steady-state operation, over a narrower RPM range, than its gasoline cousin. This allows engineers to size turbos more accurately for a diesel application. This equates typically to more stable EGT temps, and lower turbine shaft speeds. Both of which aid in turbo longevity.

Regards,
Bryan Carter

 

[SBBlue]

May have to do with the exhaust temperatures.

Gas engine exhaust temps: 1600-1800 deg F

Diesel engine exhaust temps: 800-1300 deg F

 

[gbent]

It also has a lot to do with proper turbo cool down. If any turbo engine is ran hard and quickly shut down, the heat soak from the exhaust side will overheat the lubricating oil and turn a small amount of it to coke. Over time, this will block off the oil flow. The turbo life is measured in seconds with no lubricating oil.

 

[Peter7307]

Don't overlook the factor of "driver" (a highly variable and somewhat un reliable input at the best of times !)in the logevity equation.

Most "turbo" cars seem to be driven within an inch of their lives a lot of the time.

Cheers, Pete.

 

[jgm]

A lot of commercial diesels spend their working lives runnning continuously for very long periods which is ideal for longevity. They don't do stop-start motoring with attendant cool-hot-cool cycles like so many gasoline engines

 

[patprimmer]

I don't know the numbers, but I would be very surprised if turbo petrol aero engines do not have a life expectancy to match diesel trucks, as they also are designed for durability and reliability, and their manner of operation is more regulated than is the case with turbocharged petrol engined passanger cars.

The durability is designed in by the designing engineers, not by the choice of fuel.

Also, turbochargers serv 3 different functions in each engine type.

For heavy duty diesels, it typicaly serves to improve fuel economy and reduce engine weight for a given HP rated engine

For a petrol engine, it typicaly serves to increase the HP of a given engine design.

For an aircraft, it serves to compensate for volumetric efficiency losses at high altitude

Regards
pat

 

[overmod]

Much as I hate to say it, we may never know the actual 'longevity' of most turbocharged air engines *in that service.*

There are mandated rebuilds (e.g. TBOs) at specified engine-time intervals which are well short of the effective hours-of-operation equivalents for the mileages being discussed.

While I do not doubt that component robustness and general quality are high in aeronautical applications (and cost os often little or no object!), we might also remember that light weight and packaging can be factors in design.

 

[SBBlue]

My two cents. . . . .

1) Turbochargers for spark ignition engines are really only functional at near-full to full throttle openings -- i.e., while accelerating or climbing hills. Diesels, on the other hand, have turbochargers that are not throttled and essentially work all the time. The turbos increase peak hp on gas engines and "cruise" hp on diesel engines.

2) The mandated rebuilds in aircraft are only for commercial aircraft. There are less and less piston aircraft in that particular category.

Having said that, it should be noted that the typical turbocharged aircraft engine probably won't make it to the tbo number, which may only be 1200 or 1400 hours anyway.

 

[Metalguy]

That Cummins is about 800 cu. in. and might make 350 HP, and it weighs so much you need a BIG rope to lift it.

Low stresses, lots of metal(in the right places)=long life.

 

[littlechappy]

I think heat has alot to do with the life of an engine. No matter what type of engine it is, getting to operating tempt and staying there is important. More so, on a gas engine because of the condensation that builds up after cool down. I have found that a diesel doesn't have the same issues mainly because diesels don't run at such a high temp.
I also think that the people who are buying the gas turbo's maybe pushing the engine over it limits. Diesels like gas have rev limiters on them, and seeing as the diesels stroke is much shorter than that of a gas engine, it is much harder to push that button. But it is a familiar case to see someone young and foolish pushing a turbo charged car to its limits. Sooner or later, something has to go.. I find it is more of a connecting rod than a turbo problem..
You also have a hard time finding a young person buying a diesel because they don't offer that option in little cars..

Chappy

 

[ivymike]

You also have a hard time finding a young person buying a diesel because they don't offer that option in little cars..

apparently you're in the US?

 

[Retracnic]

Diesels are indeed in relatively short supply here in the states. Maybe because many Americans are like myself. Diesel could be an option on every car, and I still wouldn't opt for it. Sure, if I needed a robust towing vehicle or a heavy duty gen set, I'd get diesel. But since I enjoy the sport of driving, diesel is rather unappealing.

And even though it's purely subjective, I just don't enjoy the sound or smell of a diesel engine. An engine that sounds like it's full of marbles and belching out clouds of smoke that reminds one of a fire in a coal mine... just isn't sexy.

"That's right baby. 1000 lbs of torque and 12 horsepower. This puppy screams all the way up to it's 2800 RPM redline. Yep, she's a real monster. You want to hold the glow plug button in, or shall I?"

Just doesn't have the same ring to it.

Regards,
Bryan Carter

 

[macangus]

Retracnic, check out the BMW diesel engines. You'd swear they were petrol if it weren't for the badge on the back...
I agree, the large diesel engines are simply designed to last.

Macangus

 

[hannaco]

Try driving the new Mercedes Benz or VW diesels. Might just change your mind. High milage, little soot, low noise, and good power.

 

[Retracnic]

I was staring at a TiAL blow-off valve I have sitting on my desk, and I thought of another reason why a turbo may last a little longer on a diesel application. My reasoning went like this:

What's the purpose of a BOV? It's to relieve pressure in the intake track when the throttle is rapidly closed. That's when it hit me, diesel engines don't have a throttle. They use fuel to modulate RPM and power output. The turbo on a diesel is not subjected to the same resonance and pressure changes as in a gasoline (petrol) engine. Which, of course, is easier on the turbo's bearings and shaft. Maybe that could be it...

Regards
Bryan Carter

 

[rmw]

Google <Fisher Tropsch>, and when the implications of what you find sink in, you will realize that we will all be driving diesels within my lifetime. With the world awash in natural gas that can't be effectively used where it is located, and the ability to make it into FT diesel, which denotes sulphur free diesel, and the current success of diesel as a motor fuel in europe, I believe FT diesel derived from natural gas, and shipped by boat is the thing to bet on.

 

[Slowzuki]

One thing unnoted: Turbo car engines generally require premium gas which they rarely get, and are riding the edge of knock/preignition all the time, with the computer and knock sensor likely saving the engine from the poor college student owner or whatnot.
Knock has been shown to strip away the boundary layer of gases that protects the piston and can eventually damage it. It also causes the flame front speeds to jump from the order of centimeters per sec to meters per sec with a corresponding increase in crank and rod loads.

The diesel cannot preignite! No crazy above design crank loads, no piston softening/ annealing etc. Well, until the owner turns up the injection pump and adds propane injection etc etc. and melts the pistons!