64 replies to this topic

[jcbc3]

Yep, the headline is correct.

According to Auto-Motor und Sport, BMW is developing an engine that utilises the waste heat from combustion to increase efiiciency in the engine by up to 15%. In short they let the exhaust through two heat exchangers that in a separate water circulation system makes steam that power a 2-stage steam turbine that's connected directly to the crank shaft. A second water circulation system draws excess heat from the cooling water to help the process of producing steam to propel the turbine. In their 4 cylinder 1.8 litre engine they claim a 14 bhp increase (the article doesn't say from what level though) or a 20 Nm increase in torque.


I work in an engineering company that designs large ammonia, fertiliser and petrochemical plants. And we have always utilised excess heat to produce steam and make our plants more energy effiecient. But must admit, that until I just read this small article in AMS I hadn't considered that it could be of any use in a car engine. But it seems to me, that it's blindingly simple, and I can't see any reason why it shouldn't work.

There was the ball. Now shoot it down, please.

Diagram

Article in AMS

[Fat Boy]

Using exhaust heat to increase the efficiency of an engine is a very common thing to do. This is a way to do so while staying within the rules(after looking at the pictures, I see it's for a street car, this means that the 'rules' are governmental, probably emissions based, not by a racing sactioning body). The common way of doing it is just a turbocharger. When compared to a conventional turbo, it's probably a really inefficient way of recovering waste heat.

The temperature drop across a turbo is much more important than the pressure drop.

[desmo]

I posted a link to an article on the Turbosteamer concept in the "Crazy Racing Engines" thread but it seems to have passed completely unnoticed. I agree this seems like an obvious idea, but the implementation is the trick. There isn't a lot of detail about how it actually is done in anything I've been able to find, just the usual shallow press release pablum.

Interesting idea, I want to learn more.

[desmo]

Originally posted by Fat Boy
Using exhaust heat to increase the efficiency of an engine is a very common thing to do. This is a way to do so while staying within the rules(after looking at the pictures, I see it's for a street car, this means that the 'rules' are governmental, probably emissions based, not by a racing sactioning body). The common way of doing it is just a turbocharger. When compared to a conventional turbo, it's probably a really inefficient way of recovering waste heat.

The temperature drop across a turbo is much more important than the pressure drop.

Except I've seen very little to convince me that turbocharging does much of anything to increase the thermodynamic efficiency or BSFC of SI engines out in the real world. If the Turbosteamer concept is inefficient compared to a turbo, then it would be a complete waste of time.

[jcbc3]

Originally posted by Fat Boy
Using exhaust heat to increase the efficiency of an engine is a very common thing to do. This is a way to do so while staying within the rules(after looking at the pictures, I see it's for a street car, this means that the 'rules' are governmental, probably emissions based, not by a racing sactioning body). The common way of doing it is just a turbocharger. When compared to a conventional turbo, it's probably a really inefficient way of recovering waste heat.

The temperature drop across a turbo is much more important than the pressure drop.

Could the two concepts be combined? Or go the whole way and put this steam concept on VW's new Turbo+compressor engine?

I seem to remember that I sometime during the eighties read an article in Road&Track about "the adiabatic engine". Wonder if that was based on something like this. Hmmmm, it must be google time now.

[alexbiker]

This concept is well proven in the field of IGCC (Integrated gassification combined cycle) coal-fired power stations. There, coal is gassified using high temperature, high pressure steam, then burnt in a gas turbine. Heat is used to form steam, which is both used for further gassification, and then to drive a three-stage steam turbine. The process overall can achieve thermal efficiencies of 50% (usual for a coal-fired station 30%ish), but is hindered by extremely high start-up costs - most of the plants are in America, where Uncle Sam is subsidising the start-up costs heavily for no good reason anyone can work out ;)

Alex

[desmo]

If a way could be economically devised to make IC engines ~50% thermodynamically efficient, that would be an almost incomprehensibly huge step forward. I assume it's practically impossible therefore

[Wuzak]

Originally posted by desmo


Except I've seen very little to convince me that turbocharging does much of anything to increase the thermodynamic efficiency or BSFC of SI engines out in the real world. If the Turbosteamer concept is inefficient compared to a turbo, then it would be a complete waste of time.

It would not be necessary to turbocharge the engine.

Use the turbine to drive a shaft connected the crank output.

A few aircraft piston engines used this concept towards the end of and after WW2. It is called Turbo Compound.

I read an article a couple of years ago that said that Keith Duckworth's first turbo engine concept for F1 was in fact a turbo compound. It was dumped in favour of anormal turbocharged engine when the FIA said it would ban it after its first race victory.

[Greg Locock]

I'd guess roughly 50% of gas turbine powered warships use this or an equivalent system.

Adding a conventional turbocharger to a conventional SI engine changes the bsfc by bugger-all, or even makes it worse. The reason is obvious if you sit down and think about it. I'm too lazy to do it again.

Since a cat is running at 700 C, and that's pretty much the temperature of an efficint steam plant, it does not seem unreasonable that you could make use of that energy. If you believe the usual figures, 30% of the energy in the incoming fuel is used to heat the exhaust, so if you manage an overall steam plant efficiency of 20 % (which in my opinion is feasible for a small add-on) then you get an effciency improvement that looks like 6%.

So, if your standard engine was 30% efficient, now its 36% efficient (ie a 20% improvement). Not bad, that's about what the Prius engine manages (37%). Or if you use it on a Prius you'd get 43%.

I don't think they'll get much out of the coolant - 110 deg c is too close to the rejection temperature - say 60 deg C worst case

Other approaches I've seen include using high temperature Peltier devices to generate electricity.

There's a long list of pitfalls with either approach.

[McGuire]

Originally posted by Fat Boy
Using exhaust heat to increase the efficiency of an engine is a very common thing to do. This is a way to do so while staying within the rules(after looking at the pictures, I see it's for a street car, this means that the 'rules' are governmental, probably emissions based, not by a racing sactioning body). The common way of doing it is just a turbocharger. When compared to a conventional turbo, it's probably a really inefficient way of recovering waste heat.

The temperature drop across a turbo is much more important than the pressure drop.

Well, something like that, but you will probably need a boost gauge:

[12.9:1]

With petroleum based fuels likely to approach $2/liter by the end of the decade, spending significantly more on efficiency will naturally follow. It seems to me that a lot of the technology needed is already on the road. various EFI Diesels, BMW's no throttle system and Audi's DFI, of course Toyota's hybrid drive. The Turbosteamer concept or similar system will certainly see the road.

I see the need as not just max efficiency, but also a small engine able to become large on cue.

The Garrett electrically assisted turbocharger, An ultra-high speed electric motor/generator drives/is driven by the turbocharger to provide boost at low engine speeds where adequate exhaust flow is unavailable or unequal to the demand. "This means an electrically driven unit can provide boost from a cold start, just off idle, or in transient response conditions, making boost totally independent of engine speed, Plus you can use the electric motor to eliminate the need for a separate wastegate and eliminate throttle lag." Then with the engine running in an efficient power range - excess energy can be redirected through the generator to provide electrical power, a direct source of high voltage for hybrid electric vehicles, say a next gen Prius like vehicle.

With this setup the turbo can be "connected" to the engine crank in a continuously variable way. Also such a turbo would interact with the CI engine in several modes, say if fitted with an oversized turbine with Variable inlet* geometry could (in full power mode) provide Boosted inlet air as well as high voltage for the electric drive motor/battery


*
Garrett's second VNT design casts the vanes as part of the housing, and uses a piston to vary the width of the chamber. Like the pivoting VNT design, the idea is to provide optimal flow to the turbocharger regardless of engine speed. Restricting the passage at low speeds increases exhaust velocity through the scroll, augmenting boost pressure. At higher engine speeds or power levels, the piston increases the nozzle width to balance exhaust flow and boost.

[McGuire]

Originally posted by jcbc3
I seem to remember that I sometime during the eighties read an article in Road&Track about "the adiabatic engine". Wonder if that was based on something like this. Hmmmm, it must be google time now.

The "adiabatic engine" was a Smokey Yunick production, and a dead end IMO. If he were here today I think he would probably say the same thing, in somewhat more sympathetic terms of course.

[McGuire]

Originally posted by desmo


Except I've seen very little to convince me that turbocharging does much of anything to increase the thermodynamic efficiency or BSFC of SI engines out in the real world. If the Turbosteamer concept is inefficient compared to a turbo, then it would be a complete waste of time.

A turbocharger will not improve BSFC or increase net efficiency because it simply pumps in more air, which requires more fuel in proportion and mainly perpetuates the same chain of inefficiencies as before. Meanwhile it generally takes some pumping work from the engine to operate the exhaust turbine. The intake compressor is pumping and heating intake air, and unless the turbine and compressor operate at greater than 100% combined net efficiency (not damn likely eh) the result will be a net decrease in engine efficiency too.

Turbocompounding is a rather different matter, as here the exhaust turbine is coupled to the crankshaft and contributes directly to engine output. If the exhaust turbine can be optimally calibrated to operate only on "excess" blowdown the result is an improvement in net efficiency... with some caveats. One problem is the disparity between crank speed and turbine speed, each relative to load, and requiring a fluid coupling of some kind (not known for their high efficiency either hmm). Running the engine at constant speed/load simplifies these issues enormously, for example in aircraft. The last of the large piston airliners like the Constellation used turbocompounding quite effectively. These were the first and probably the only piston airliners capable of flying the USA coast-to-coast nonstop.

It seems to me the BMW steam turbocompound stage has possibilities...if it is using exhaust heat only to heat water, introducing no exhaust backpressure and not robbing the engine of heat energy, then it is in effect only picking up the "free" nickels and dimes otherwise lost out the tail pipe. And thus anything it can gain and put back at the crankshaft will produce a net gain in efficiency... minus the weight it adds to the vehicle, losses in the fluid coupling, etc.

It seems to me that in this application steam has the advantage of flexibility, and the disadvantage of low efficiency. That is what killed the steam automobile, despite some intriguing characteristics in other areas.

Personally I still like Mr. Locock's turbo-alternator, especially in a hybrid application. We can pulse-width modulate the thing relative to available backpressure, alternately throwing it against the batteries and freewheeling it as desired.

[J. Edlund]

Originally posted by desmo
Except I've seen very little to convince me that turbocharging does much of anything to increase the thermodynamic efficiency or BSFC of SI engines out in the real world. If the Turbosteamer concept is inefficient compared to a turbo, then it would be a complete waste of time.

It is possible to increase the efficiency using turbocharging; however since spark ignition engines are knock limited it isn't possible in the way as it is with for example diesels. The increase in diesel efficiency comes from that turbocharging can for example double the IMEP with no significant change of FMEP, and since BMEP = IMEP - FMEP, BMEP will be greater in comparison to IMEP which shown an increased efficiency. Note that fuel consumption follow IMEP, while output follows BMEP.
However, a turbocharged gasoline engine can and often do provide a lower fuel consumption for a certain power level in daily driving since a properly designed (downsized) turbocharged engine will have a better BSFC at low loads and a little worse BSFC at high loads but since most driving is done at low loads there is a positive gain. Further information about this can be found in Watson & Janotas "Turbocharging the Internal Combustion Engine", Garrett Engine Boosting Systems "Smart Boosting Systems e-TurboTM and e-ChargerTM “New” Frontier?", articles about BMW's coming turbocharged engines, and probably many other articles and papers.

Using turbocompound can directly increase efficiency, but it is impossible to design a turbine that will work at both low loads and full load. Diesels are a bit better here since they haven't a throttle that limit air flow at low speeds. A diesel does also have a shorter rpm range which also make turbine design easier.
The loss caused by the flow restriction have been shown by for example NACA to be almost non existing.

To heat water with the exhaust is common in for example ships. To produce power from it using a turbine there are however one disadvantage in comparison to using the exhaust directly; that is that the temperature is much lower hence will the efficiency of the system also be much lower. The advantage in comparison to using a turbine directly as I see it is that the water can act as a buffer and the flow over the turbine can be controlled.

[JwS]

Just a related curiousity that might go toward the "its all been done before" file. I remember visiting the Ford museum as a boy and seeing a compound engine that was used as a power unit at the River Rouge plant when they first built it (1930's??). It consisted of two enourmous cylinders on a common crank, the first a fuel powered (not sure what kind) cylinder and the second a steam cylinder that ran off the waste heat of the first. The thing was of course huge, maybe 50 feet long, it was a horizontal parallel twin layout. Don't know how well it worked.
JwS

[NTSOS]

Using turbocompound can directly increase efficiency, but it is impossible to design a turbine that will work at both low loads and full load.

I don't care about efficiency, I'm a hotrodder.

I have always thought about a pair of exhaust turbines geared to the flywheel like a Connie in conjunction with a modest crank driven supercharger would make a killer street driven acceleration package for my SB Chevy.

John

[McGuire]

Didn't anyone like the "boost gauge"? I figured you Detroit iron guys would get a kick out of it.

[NTSOS]

Didn't anyone like the "boost gauge"? I figured you Detroit iron guys would get a kick out of it.

Actually, I enjoyed the boost gauge a little too much and didn't want to seem overly enthusiastic.....just in case!

John

[desmo]

It needs a faux carbon fiber face and a neon purple needle I think...

[Wuzak]

What about using the exhaust heat to power a Stirling cycle motor?

[Greg Locock]

Nothing. In principle. For stationary systems.

A 150 kW Stirling engine is about the same volume and mass as a 3000 kW diesel engine.

[dosco]

Originally posted by McGuire
Didn't anyone like the "boost gauge"? I figured you Detroit iron guys would get a kick out of it.

I copied the pic to my PC and sent it to some motorhead buddies, who enjoyed it.

We didn't get the "C16" reference, though.

(and yes, it needs some faux CF and some other trinkets to "trick it out d00d")

[Viss1]

Originally posted by McGuire
Didn't anyone like the "boost gauge"? I figured you Detroit iron guys would get a kick out of it.

I found it amusing... there should also be one for "common issues with every aftermarket turbo project" (ie. "don't get on it too hard, the upper IC hose is leaking a little" or "don't get off the boost too quickly, the hose likes to come off").

[Fat Boy]

Originally posted by dosco

We didn't get the "C16" reference, though.

(and yes, it needs some faux CF and some other trinkets to "trick it out d00d")

Just so Mac knows I got the joke. C-16 is a race fuel from VP., if the guy in on pump gas, he can only run 10 psi boost, but on C-16 he can squeeze it to 30.

Pretty funny.

There needed to be something on there for 'The Stage 5 Chip'.

Have you seen 'Race Engineer's Bingo'?

[Fat Boy]

"I got you on the loser flyby"

That is pretty classic.

[dosco]

Originally posted by Fat Boy
C-16 is a race fuel from VP., if the guy in on pump gas, he can only run 10 psi boost, but on C-16 he can squeeze it to 30.

Ah. Heh.

There needed to be something on there for 'The Stage 5 Chip'.

That would have been good. Perhaps you can update the jpeg?

Have you seen 'Race Engineer's Bingo'?

No. Enlighten me.

[dosco]

Is the "drift" a reference to "Formula Drift?"

I'm on the fence about Formula Drift. On the one hand, on the whole it seems uber-stupid. On the other, it actually takes some skill to oversteer that much and drive fast. Back on the first hand, the "success criteria" seem to be rather obtuse....things like "amount of smoke" and "drift angle."

Hrmmmm....

[NTSOS]

"I got you on the loser flyby"

Please explain!

John

[McGuire]

For years I had a system diagnostic tree chart on the wall next to my desk. Went something like this:


Did you **** with it? Yes/No

(branch)

Did anyone SEE you **** with it? Yes/No



and so on...I will have to look around and see if I still have it. Solid technical material.

[Fat Boy]

The loser flyby is when you've beaten a guy on a street drag race, and after a fair distance you've got a few car lengths ahead. Basically, you've proven your point. So you let off. After you let off, the other guy stays on it and blasts by as you're slowing down.

When I was young and imprudent I had a reasonably fast street car. It looked like hell, but I had polished the turd to the best of my ability. Anyway, being the car nerd that I am I had a good motor, but also had big brakes that were taken off of a late model stock car. If I was faster than the guy I was doing my stop light grand prix with, then I'd stay in the gas until it was going to be tough for me to stop. I'd do this knowing that my car could stop pretty damn well. I would get one hell of a chuckle watching people trying to stop with bad brakes _after_ doing the loser flyby. You could sucker some of them clean through the next intersection all locked up.

Race Engineers Bingo is a hand-drawn thing that I saw which was set up in a 5X5 grid. Each square has a driver's excuses, like, "I didn't get a clean lap in traffic", "The brakes didn't come in right", "The gearing is wrong", "The wheel is off-center", "I think something's messed up in the diff", "I got a flat spot", "The track's still green", "It pulls to one side", "We're down on power", etc. As you're doing your post session debrief you're supposed to see if you can get 5 in a row on the grid. If so, you win the Race Engineer's Bingo game vs. your teammate and fellow engineer having the same discussion.

At the bottom of the sheet was quotes from a bunch of engineers who were supposedly 'happy customers'. I believe Halliday was quoted as, "I started setting the car up wrong just to win the bingo game!"

[Fat Boy]

Originally posted by dosco
I'm on the fence about Formula Drift.

I'm not. I love it. Not because it's racing. It's not. It's a bunch of gearheads having a good time. It's what 1/2 the paddock does on their way to the hotel every night. They're really not going very fast at all. They're cars are set up to pretty much do what they want it to, and away they go.

I've seen them doing their thing at tracks on race weekends. They show up at noon. Put on a couple shows between sessions, and they're at the bar from 6pm to 6am with hottest little tramps they can find. Oh ya, and they actually get sponsored to do it.

What's not to like?

[dosco]

Originally posted by Fat Boy
I'm not. I love it. Not because it's racing. It's not. It's a bunch of gearheads having a good time.

That's cool.

I've seen them doing their thing at tracks on race weekends. They show up at noon. Put on a couple shows between sessions, and they're at the bar from 6pm to 6am with hottest little tramps they can find. Oh ya, and they actually get sponsored to do it.

What's not to like?

I guess. It's hard to say for me.....

1. I don't have a decent/powerful/cool car, so I can't really appreciate it from a "driver's perspective." Mostly cause I don't have jack for time and money....at the rate I'm going, I'm not sure I'll ever have a decent ride (not saying the cars I have are hogsters, just not "fast" or "rodded" or whatever).

2. I don't like the "hype" that surrounds it all that much. At least not yet....I'll watch some more on the tube and think about it some more.

[McGuire]

I don't get drifting, must be a generational thing, but since FB has described it in such an appealing way I guess I will give it another try.

[shaun979]

I appreciate drifting, but I don't like the crowd around it. It is a crowd shallower than many other forms of competitive driving.

[McGuire]

Originally posted by shaun979
I appreciate drifting, but I don't like the crowd around it. It is a crowd shallower than many other forms of competitive driving.

Well... if the ladies are as pleasantly shallow as FB suggests, perhaps it is worth looking into.

[McGuire]

Originally posted by Fat Boy
When I was young and imprudent I had a reasonably fast street car. It looked like hell, but I had polished the turd to the best of my ability. Anyway, being the car nerd that I am I had a good motor, but also had big brakes that were taken off of a late model stock car.

Where I came up we had to have good brakes.... running on Enterprise Blvd, Corduroy Rd, I-696... what a time that was, late '60s, early '70s. For awhile there people were taking stuff out the back doors and putting it on the street. Cars tooling Woodward Ave. with manufacturer plates, it was too funny. There were a couple guys who had actual factory deals. It can never be repeated, guess I was just lucky to be there and see it and be in it.

This will sound really sick but I never quite got it out of my system... I have a Bandit 1200 turned up a little and every so often I will take it around the bike racing haunts. This is blatant braggery but I have to share...one night at the local pop stand I overhear two kids talking behind me. One says, "who is that old f***er with the Suzuki? What is he doing here?" The other says, "I wouldn't worry about it, you aren't gonna beat him." hee hee hee. Made my day/week/year. I am so JUVENILE.

[hydra]

Originally posted by J. Edlund


It is possible to increase the efficiency using turbocharging; however since spark ignition engines are knock limited it isn't possible in the way as it is with for example diesels. The increase in diesel efficiency comes from that turbocharging can for example double the IMEP with no significant change of FMEP, and since BMEP = IMEP - FMEP, BMEP will be greater in comparison to IMEP which shown an increased efficiency. Note that fuel consumption follow IMEP, while output follows BMEP.
However, a turbocharged gasoline engine can and often do provide a lower fuel consumption for a certain power level in daily driving since a properly designed (downsized) turbocharged engine will have a better BSFC at low loads and a little worse BSFC at high loads but since most driving is done at low loads there is a positive gain. Further information about this can be found in Watson & Janotas "Turbocharging the Internal Combustion Engine", Garrett Engine Boosting Systems "Smart Boosting Systems e-TurboTM and e-ChargerTM “New” Frontier?", articles about BMW's coming turbocharged engines, and probably many other articles and papers.

Using turbocompound can directly increase efficiency, but it is impossible to design a turbine that will work at both low loads and full load. Diesels are a bit better here since they haven't a throttle that limit air flow at low speeds. A diesel does also have a shorter rpm range which also make turbine design easier.
The loss caused by the flow restriction have been shown by for example NACA to be almost non existing.

To heat water with the exhaust is common in for example ships. To produce power from it using a turbine there are however one disadvantage in comparison to using the exhaust directly; that is that the temperature is much lower hence will the efficiency of the system also be much lower. The advantage in comparison to using a turbine directly as I see it is that the water can act as a buffer and the flow over the turbine can be controlled.

Gentlemen,
The main reason turbos increase efficiency is because they raise peak combustion pressure (for a given compression ratio), increasing P3/P1 and the area under the P-V curve... Mechanical efficiency would also increase, but not as much as you would expect, as the piston skirt and crank bearings would have to be upsized (assuming they were optimized in the NA engine) to handle the increased cylinder pressures...

[Christiaan]

Pardon me guys, I have not been able to understand what people call Turbo Efficiency. Are you talking about it's effiencincy as a compressor or aare you talking about its efficiency for the engine. If so, what size engine do you compare it with? An equivalent normally aspirated engine or an engine of the same capacity?

In addition have been fed two schools of thought on combustion of fuel. One says that the burning efficiency increases as the air/fuel ratio increases beyond the stoichimetric ratio. This I was taught from an A'Level Chemistry textbook. From that standpoint turbocharging should increase an engines efficiency. My first Thermodynamics lecturer supported this idea and went on to say that the leaner the mixture, the more efficient the engine. The limit being that lean mixtures have a high thermal conductivity so the engine will overheat if the mixture is too lean. However, my IC Engines lecturer said that the "burnability" decreases rapidly, and flame propagation becomes a problem. So when turbocharging you may not go below stoichiometric mixtures.

Which is it?

[Wuzak]

Originally posted by Christiaan
Pardon me guys, I have not been able to understand what people call Turbo Efficiency. Are you talking about it's effiencincy as a compressor or aare you talking about its efficiency for the engine. If so, what size engine do you compare it with? An equivalent normally aspirated engine or an engine of the same capacity?

The true measure of efficiency of an engine is how much energy you get out from the potential energy you put in.

Would that be the specific fuel consumption, measured in kg(fuel)/kW(output)/hr? Or in Imperal measure, lb/hp/hr?

[Greg Locock]

...which we often reduce to a bastardised thermodynamic efficiency by dividing by the calorific value of the fuel, 43 MJ/kg. For some theoretical reason that's not the perfect answer, but for all practical purposes it is fine.

[hydra]

Originally posted by Christiaan
In addition have been fed two schools of thought on combustion of fuel. One says that the burning efficiency increases as the air/fuel ratio increases beyond the stoichimetric ratio. This I was taught from an A'Level Chemistry textbook. From that standpoint turbocharging should increase an engines efficiency. My first Thermodynamics lecturer supported this idea and went on to say that the leaner the mixture, the more efficient the engine. The limit being that lean mixtures have a high thermal conductivity so the engine will overheat if the mixture is too lean. However, my IC Engines lecturer said that the "burnability" decreases rapidly, and flame propagation becomes a problem. So when turbocharging you may not go below stoichiometric mixtures.

Which is it?

Thermal/standard air-cycle efficiency increase with lean mixtures (equivalence ratio ) increases the leaner the mixture gets, starting off at 1.3 and approaching 1.4. Turbocharging does indeed increase a Diesel engine's efficiency, not just because of the increased maximum P3, but because the higher temperatures and pressures allow it to use even leaner mixtures, like 30:1 instead of 25:1 (for instance), increasing thermal efficiency for the reason I mentioned earlier. The limit you speak of only applies to SI engines operating between an A/F ratio of 11:1 and 14.7:1 , which is only lean in a relative, and not absolute sense. Above 15:1 the heat generated by combustion falls much more rapidly than the thermal conductivity increases, leading to a net DECREASE in temps. The stable combustion limit for conventional SI engines being around 18:1 or so...

As an aside, I've said this before and I'll say it again. The ultimate engine concept in my opinion is a turbocharged, uniflow-scavenged, 2-stroke diesel - preferably in a compact and stiff 180-degree V6 configuration (with a 3-throw crank) producing 150bhp/L and bsfc

Possible future developments would include a VG/VN Turbo, and (Oh-joy! Oh-rapture!) sleeve-valves... Now back to reality again

[Wuzak]

A question about gas turbines: does a gas turbine need to maintain the fuel mixture as for a piston SI engine, or can it be run very lean (ie leaner than stoichometric)?

I was looking up some data on turboshafts the other day, and I discovered one that produced approximatel 1800hp in a package that was about 500lb in weight. I did a basic calculation using its SFC, and it turns out that at maximum hp it used about the same fuel per hour as the 1000bhp engine in the Bugatti Veyron.

[McGuire]

Originally posted by hydra
Gentlemen,
The main reason turbos increase efficiency is because they raise peak combustion pressure (for a given compression ratio), increasing P3/P1 and the area under the P-V curve...

So does a supercharger increase efficiency as well?

[Paolo]

Originally posted by hydra
for a given compression ratio

Yet, I seem to remember that compression ratios on turbo engines are far lower than on atmospheric engines...
This discussion brings me back to my first thread ever... nostalgia...

http://forums.autosp...&threadid=12837

[dosco]

Originally posted by Wuzak
A question about gas turbines: does a gas turbine need to maintain the fuel mixture as for a piston SI engine, or can it be run very lean (ie leaner than stoichometric)?

I learned that the fuel-air ratio is generally stochiometric, although you'll find that most gas turbines use a "layered" approach where the "core" of the fuel injection is stochiometric or slightly rich, and the outer postion of the injection pattern is lean. The idea being the outside of the burn area is supposed to be cooler than the core, so as not to melt the combustor.

There are all kinds of research and experimentation on this, though, so as to reduce pollution (particulates, NOX, etc). Google the GE Aero Engines website, there are bits and pieces of info there about their work.

I was looking up some data on turboshafts the other day, and I discovered one that produced approximatel 1800hp in a package that was about 500lb in weight. I did a basic calculation using its SFC, and it turns out that at maximum hp it used about the same fuel per hour as the 1000bhp engine in the Bugatti Veyron.

Well, the specific power of a turbine is pretty much a function of its pressure ratio (akin to compression ratio of a piston engine). Many of the older engines were far less efficient than pistons, newer ones (that have Full Authority Digital Engine Controls, full VSV systems, etc etc) generally are substantially more efficient. The primary reason for their use in aviation is mostly a function of reliability - gas turbines are way way more reliable than their piston engine "equivalents."

[hydra]

Originally posted by McGuire


So does a supercharger increase efficiency as well?

If you don't take CMEP losses into account, yes it does! I realize that's a completely unrealistic scenario, but my point was that increasing the ratio of P3/P1 by itself will INCREASE thermodynamic efficiency, but I will admit that in practice that just doesn't happen with SI engines, either supercharged or turbocharged. A diesel engine on the other hand, would probably benefit from running an efficient supercharger running lowish boost and decent intercooling, but a turbo would definitely be a better choice (power, efficiency, etc) for the money...

[McGuire]

Originally posted by hydra



If you don't take CMEP losses into account, yes it does! I realize that's a completely unrealistic scenario, but my point was that increasing the ratio of P3/P1 by itself will INCREASE thermodynamic efficiency, but I will admit that in practice that just doesn't happen with SI engines, either supercharged or turbocharged.

Turbocharging (or supercharging) does not increase the net efficiency of an SI powerplant.

Also, while turbocharging increases cylinder pressure, turbocompounding (the subject of this thread) does not.

[Fat Boy]

Originally posted by shaun979
I appreciate drifting, but I don't like the crowd around it. It is a crowd shallower than many other forms of competitive driving.

I would see your shallow and raise you 2 stupids. The crowd and the participants are pretty much the same people. What I like about it is that it's a bunch of yahoo's going out and raising hell.

Watching a proper race driver run a qualifying lap is 100 times more impressive for me to watch, but I get a kick out of watching some moron drive his car sideways for 200 yards down a straight-away with smoke pouring off the tires. I would say that a comparison in basketball would be a three-pointer vs. a slam dunk. The 3-pointer is a hell of a lot tougher to do for a pro and is more meaningful in the game, but it's still cool to watch Shaq man-handle a dunk.

Racing can get a bit serious at times. It's nice to have some comic relief and watch some guys tear **** up. And let's face it, you don't get many nice looking women walking around a normal paddock. Maybe one here or there. It seems like these guys all have about a 1/2 dozen with them. Now _that's_ impressive!

[shaun979]

Originally posted by Fat Boy
[B]I would see your shallow and raise you 2 stupids.

LOL

The crowd and the participants are pretty much the same people.

Except the drivers do have some driving skill... some of them in extreme amounts too. The crowd is just drawn by the spectacle and most have no idea what driving is. All they know is it's cool.

Watching a proper race driver run a qualifying lap is 100 times more impressive for me to watch, but I get a kick out of watching some moron drive his car sideways for 200 yards down a straight-away with smoke pouring off the tires. I would say that a comparison in basketball would be a three-pointer vs. a slam dunk. The 3-pointer is a hell of a lot tougher to do for a pro and is more meaningful in the game, but it's still cool to watch Shaq man-handle a dunk.

Agreed

And let's face it, you don't get many nice looking women walking around a normal paddock. Maybe one here or there. It seems like these guys all have about a 1/2 dozen with them. Now _that's_ impressive!

I prefer quality over quantity 1 lady (mind and character) > 10 skanks (makeup and silicone)

[red300zx99]

Originally posted by shaun979

I prefer quality over quantity 1 lady (mind and character) > 10 skanks (makeup and silicone)

Which race is the lady at?