Silverbullet86
Mechanical
I think my Thermodynamics text book needs to be rewritten now.
Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Turbine Engine: No Pistons, no lube, 30% better on gas! 1
- Thread starter Silverbullet86
- Start date
- Status
I think my Thermodynamics text book needs to be rewritten now.
I doubt there's anything going on here that violates laws 0, 1, or 2. (although it may be claimed that something is)
there's at least one guy over at who would enjoy talking about this at length.
there's at least one guy over at who would enjoy talking about this at length.
Its hard to believe there is improved fuel effiency when there are flames coming out of the exhaust in the videos.
This engine versus a typical gas turbine could show improved effiecency because it uses a positive displacement air compressor. The power turbines are closed impellar, don't know how they handle high temp and loads.
This engine versus a typical gas turbine could show improved effiecency because it uses a positive displacement air compressor. The power turbines are closed impellar, don't know how they handle high temp and loads.
btrueblood
Mechanical
"Jets/turbines highly inefficent. "
Um, well, no. Turbines are generally more efficient than piston engines at fixed power outputs, and can operate for longer durations between overhauls. That's why you see a lot of newer, large, fixed power installations using gas turbine engines.
But, turbines don't throttle well, i.e. they are relatively inefficient when operating below their design power output level. Since operation across a wide range of loads/speeds is a necessary attribute for automotive engines, turbines don't compare well to pistons.
Um, well, no. Turbines are generally more efficient than piston engines at fixed power outputs, and can operate for longer durations between overhauls. That's why you see a lot of newer, large, fixed power installations using gas turbine engines.
But, turbines don't throttle well, i.e. they are relatively inefficient when operating below their design power output level. Since operation across a wide range of loads/speeds is a necessary attribute for automotive engines, turbines don't compare well to pistons.
btrueblood
Mechanical
btrueblood
Mechanical
oops. A little hard to find this on their site:
Chrysler I think it was went as far as consumer testing a turbine-powered passenger car around the early 60's. Really neat project. This concept is supposedly for HD application, but investors would be wise to study the Chrysler experience and determine why the lessons learned there don't apply for any proposals of new applications . . .
-
1
- #10
GregLocock
Automotive
I've driven (very briefly) a gas turbine car. Rover built several. There was also at least one Indy car that had a GT.
It is just conceivable that a GT hybrid might make sense, but I think that a conventional turbo-diesel is a better bet.
Small GTs just aren't very efficient.
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
It is just conceivable that a GT hybrid might make sense, but I think that a conventional turbo-diesel is a better bet.
Small GTs just aren't very efficient.
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
btrueblood
Mechanical
Greg, that conventional wisdom is becoming dated. Capstone has 30kW microturbines with a published electrical output efficiency of 31%, in single-stage versions (ok, running on natural gas, not kerosene, but still that's a pretty nice figure for something so small). There's room for better efficiency from their models, from some type of two-spool arrangement or just extra compressor stages.
Again, the efficiency of a GT drops like a rock when it's throttled, whereas a piston engine can operate over a comparatively wider power range with reasonable efficiency. A hybrid that took advantage of the throttling ability could perhaps have less battery weight to lug around, giving better vehicle mileage?
Again, the efficiency of a GT drops like a rock when it's throttled, whereas a piston engine can operate over a comparatively wider power range with reasonable efficiency. A hybrid that took advantage of the throttling ability could perhaps have less battery weight to lug around, giving better vehicle mileage?
BrianPetersen
Mechanical
In a 30kW package size optimized to run on natural gas, 31% thermal efficiency can be be beat by a spark-ignition piston engine, and as you note, it will maintain close to that efficiency over a much broader range of power output. (Natural gas will tolerate a very high compression ratio.)
btrueblood
Mechanical
31% - a naturally aspirated piston engine won't beat that by much, it would require turbocharging or supercharging to get there (I could very well be wrong, but I'm assuming standard production tolerances, not blueprinted racing engines). Such additional machinery would be equivalent to adding spools/stages to the capstone turbine, and is an unfair comparison in my opinion. What is not unfair is to compare costs, last time I had good numbers (~7 years ago) the microturbines were about 10x the cost of piston engines, with comparable efficiencies. The only way they make sense is in terms of noise and maintenance requirements.
BrianPetersen
Mechanical
Production motorcycle engines are in that range at their best BSFC point, running on gasoline. Normally aspirated. Natural gas will allow more compression for a little higher efficiency.
GregLocock
Automotive
No, the Prius engine has a best operating point of 37%, and is above 30% for its entire operating range apart from idle.
No turbo.
Automotive diesels can achieve 41% when turbocharged.
Cheers
Greg Locock
SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
No turbo.
Automotive diesels can achieve 41% when turbocharged.
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.Most natural gas engines is the 30kW range aren't turbocharged so the microturbine efficiency numbers would be tough to beat (most MGEs over 100kW ARE turbocharged though). A natural gas engine less than 100kW is typically used in a wellhead-type gas pumping installation where the pressure and flowrate (read: engine load) vary considerably, so a microturbine would not a be ideal for the application (hence their limited (!?) use here). The larger gathering/pumping applications have far less variance in the pressure and flowrate so a turbine would win due to efficiency and maintenance (hence their regular use here). Also, btrueblood stated 31% as the ELECTRICAL efficiency so a generator of 90% efficiency would put it on par with the pistons; which seems reasonable to me for an AC generator.
btrueblood
Mechanical
Hm, ok, thanks for that waking up, Greg. The Prius engine has a bit of "extra tech" on it, in the way of VVT, but it's a fair comparison.
I meant to say that boost would be required to beat the turbine "by a significant amount", my (out of date!) numbers said 30% was about where a typical nat-aspirated gasoline engine can run.
Yes, the capstone nubmer is an electrical output efficiency. They are known in the GT biz as kind of weird, they never quote the turbine's shaft power/efficiency figures, only system figures. Part of their story is a very efficient electrical generation control system (I imagine lots of digital circuitry and inverter stuff), so if that were adapted to the Prius engine, perhaps we're still talking close numbers, with the Prius beating it handily by several points.
My point is (was) that only 20 years ago, "small" turbines were in the 1000 kW range, and had efficiencies in the 20's. They've come a long ways in making smaller versions with good efficiency. But that rising tide lifts all boats, and it appears piston engines still compete well, and will likely continue to do so, in the "small" sizes needed for typical (land) automotive uses.
Regarding throttling - a GT just can't idle, it must run at near the same mass flow of air, or the turbine stalls. You can reduce the fuel flow only so far before the burners won't stay lit (ok, with hydrogen fuel I could keep them lit...but let's not go there). There are some fancy ideas regarding bypass valves and multi-spool designs, but you might as well talk about multi-engines and boosted piston engines then.
A piston engine, however, can idle at a very small fraction of its best-consumption rpm and mass flow, and so can idle with comparatively low fuel consumption. And starting/restarting a turbine is a fuel-consumptive, slow process in comparison to piston engines also.
So, no, I agree with Greg that they won't be seen in large numbers on the roads very soon.
So, let's talk rocket engines instead: strap a solid-fuel booster onto your favorite chassis, light the fuse...as long as you didn't have any stoplights or turns, you could boost to Mach 3, and coast the rest of the way...
I meant to say that boost would be required to beat the turbine "by a significant amount", my (out of date!) numbers said 30% was about where a typical nat-aspirated gasoline engine can run.
Yes, the capstone nubmer is an electrical output efficiency. They are known in the GT biz as kind of weird, they never quote the turbine's shaft power/efficiency figures, only system figures. Part of their story is a very efficient electrical generation control system (I imagine lots of digital circuitry and inverter stuff), so if that were adapted to the Prius engine, perhaps we're still talking close numbers, with the Prius beating it handily by several points.
My point is (was) that only 20 years ago, "small" turbines were in the 1000 kW range, and had efficiencies in the 20's. They've come a long ways in making smaller versions with good efficiency. But that rising tide lifts all boats, and it appears piston engines still compete well, and will likely continue to do so, in the "small" sizes needed for typical (land) automotive uses.
Regarding throttling - a GT just can't idle, it must run at near the same mass flow of air, or the turbine stalls. You can reduce the fuel flow only so far before the burners won't stay lit (ok, with hydrogen fuel I could keep them lit...but let's not go there). There are some fancy ideas regarding bypass valves and multi-spool designs, but you might as well talk about multi-engines and boosted piston engines then.
A piston engine, however, can idle at a very small fraction of its best-consumption rpm and mass flow, and so can idle with comparatively low fuel consumption. And starting/restarting a turbine is a fuel-consumptive, slow process in comparison to piston engines also.
So, no, I agree with Greg that they won't be seen in large numbers on the roads very soon.
So, let's talk rocket engines instead: strap a solid-fuel booster onto your favorite chassis, light the fuse...as long as you didn't have any stoplights or turns, you could boost to Mach 3, and coast the rest of the way...
GregLocock
Automotive
A graph of the weight of battery required versus the powerpack weight for a microturbine and a Prius type installation would be interesting. As you make the battery bigger the advantage would swing towards the turbine, since the battry could be used to cover for the operating condition where the turbine should not be used.
I'm assuming that the turbine set has a better power to weight ratio than the pseudo-Atkinson engine in the Prius, note hat it also needs a gearbox or traction motor rather larger than the Prius'.
Cheers
Greg Locock
SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
I'm assuming that the turbine set has a better power to weight ratio than the pseudo-Atkinson engine in the Prius, note hat it also needs a gearbox or traction motor rather larger than the Prius'.
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
btrueblood
Mechanical
But, that battery weighs a lot, and would take the system weight well over the Prius' for a similar output power, which would impact the mileage?
Also, I had another look at their so-called hybrid vehicle "solution", which burns diesel/kerosene. 25% electrical efficiency, at 29 kW output.
Worse, I don't think these meet CARB standards, and the exhaust temperature may be too low to "light off" a catalytic converter:
NOx Emissions @ 15% O2 < 35 ppmvd
NOx/Electrical Output 0.846 g/bhp-hr (< 2.5 lb/MWh)
Exhaust Gas Temperature 275?C (530?F)
And the kicker - that device weighs 1300 lbs (with the genset).
Dunno why this version shows with a recuperator, unless they are adding on a steam turbine to pull some work out of the exhaust heat?
Ah well. Reality sets in again.
Also, I had another look at their so-called hybrid vehicle "solution", which burns diesel/kerosene. 25% electrical efficiency, at 29 kW output.
Worse, I don't think these meet CARB standards, and the exhaust temperature may be too low to "light off" a catalytic converter:
NOx Emissions @ 15% O2 < 35 ppmvd
NOx/Electrical Output 0.846 g/bhp-hr (< 2.5 lb/MWh)
Exhaust Gas Temperature 275?C (530?F)
And the kicker - that device weighs 1300 lbs (with the genset).
Dunno why this version shows with a recuperator, unless they are adding on a steam turbine to pull some work out of the exhaust heat?
Ah well. Reality sets in again.
globi5
Mechanical
- Oct 10, 2005
- 281
Btw, this small XR 50 rotary engine produces 31kW at a relatively low 7800 1/min weighing only 15 kg:
If it were combined with a turbo charger it could produce the same amount of power at a lower rpm and thus increase durability and efficiency. However, durability might not be this important in an application where the combustion engine is only needed to extend the range of an electric vehicle (and thus not be operated as frequently and extensively as in a normal car (GM Volt)).
Keep in mind, a piston or rotary engine also has no need for a reduction gear to operate the generator.
A piston or rotary engine with turbo is principally comparable with a gasturbine with a moving combustion chamber allowing higher pressure ratios and higher peak temperatures. Rolls Royce even patented a aircraft gasturbine concept with an integrated rotary engine:
(Although the drawing does not make much sense, as the airflow produced by the axial flow compressor of the gasturbine is obviously much higher than that of the relatively small rotary engine).
GM produced a Hybrid-Prototype with a series Gasturbine producing 40 kW at a weight of 100 kg for the entire gen-set:
If it were combined with a turbo charger it could produce the same amount of power at a lower rpm and thus increase durability and efficiency. However, durability might not be this important in an application where the combustion engine is only needed to extend the range of an electric vehicle (and thus not be operated as frequently and extensively as in a normal car (GM Volt)).
Keep in mind, a piston or rotary engine also has no need for a reduction gear to operate the generator.
A piston or rotary engine with turbo is principally comparable with a gasturbine with a moving combustion chamber allowing higher pressure ratios and higher peak temperatures. Rolls Royce even patented a aircraft gasturbine concept with an integrated rotary engine:
(Although the drawing does not make much sense, as the airflow produced by the axial flow compressor of the gasturbine is obviously much higher than that of the relatively small rotary engine).
GM produced a Hybrid-Prototype with a series Gasturbine producing 40 kW at a weight of 100 kg for the entire gen-set:
- Status
Similar threads
- Question
