To "Turbo Time" or not??" That is the Question

Roachie
My understanding of it is it's not the heat at which the turbo shuts down at, it's the speed

Most turbos run an oil film bearing, supplied by the engine oil pump. when the engine is shut down there is NO oil.
Premature shut down will cause the bearing to fail and the the turbo

Most turbos will be runing at 2 to 3 time engine rpm

Heats got F all to do with if.

but it's alway a good thing to heat up an engine as wall as cool down an engine

Richard

Hi there Sam just wondering where your located at(town) Due you live in the Penrith area as your vehicle looks familiar. Regards Steve M

Funny how the law can and is interpretted ,, it is NOT illegal in Qld to have and use a turbo timer as long as the vehicle is an AUTOMATIC , left in park/handbrake on and locked.

No, thats my fault.

Rephrase slightly.

Having one fitted ISN'T , in itself "illegal" all though frowned up by Insurance Co's , its the actual USE of them that this.

Simply , you cant walk away from a vehicle with the motor running , REGARDLESS , of why it is.

eg, TT, the shops , Pizza Shop etc.

TT's are the most prone for that.

I was given the same advice when I had my turbo fitted to my 80 Series. If I have done a long run on the highway, I just wait a few minutes when I pull up - it usually takes the wife and kids this long to sort themselves out anyway!!!

Just hope your insurance company is as obliging

Hey Flappa, What's the issue with the insurance companies?

Simply you are walking away from a vehicle that still has the motor running , and out of gear.

The biggest risk would be it running away , either by brakes failing , or being bumped into gear somehow.

Someone once told me , there is also a risk of it being stolen ???? I dont know how , but anyway .

I understood PG to state the he is happy to sit in the vehicle until it cools down so therefore he is not leaving his vehicle unattended and running. I use a turbo timer on my 4.2 Patrol and let it run down after a heavy run for about 1 minute. Normally I switch the vehicle off and then get organised and the last thing I do is switch of the timer manually.
As for leaving the vehicle out of gear, after 20 years in the Army and driving diesel vehicles the policy was to always leave diesel vehicle OUT of gear and petrol vehicles in gear. Something which I still do - the vehicle does have a handbrake. If its parked on a steep decline I turn the wheel into the kerb and if at all concerned (and I remember) then I will put it in gear

>>> I understood PG to state the he is happy to sit in the vehicle until it cools down so therefore he is not leaving his vehicle unattended and running.

they why bother with a timer? save yourself a couple a hunge $

Hey Truckster, if you read my threads you would see I said "Common sense must prevail though, I will sit in the vehicle for a couple of minutes and let it cool down IF I am in the middle of a city OR parked on a steep incline"

The driveway is the handiest place to use it, got the top off a cold one before the engine shuts down, now that's GOT to be a good thing ;-)

Cheers

John
Your on the ball it's not the heat at which the turbo shuts down at, it's the speed

Most turbos run an oil film bearing, supplied by the engine oil pump. when the engine is shut down there is NO oil.
Premature shut down will cause the bearing to fail and the the turbo

Most turbos will be runing at 2 to 3 time engine rpm

Heats got F all to do with if.

but it's alway a good thing to heat up an engine as wall as cool down an engine

Richard

Hi Guys,

Sorry Richard, but I must disagree. Heat has everything to do with it.

True, most diesel turbos run on plain bearings, which rely on oil film lubrication but also oil COOLING. As another poster said, modern automotive turbos are very low inertia compared to the relatively big, heavy types on agricultural machinery. They slow down very quickly when the throttle is closed and will be at their 'idle' speed almost as soon as the engine is. With agricultural machinery, stalling from full-load causes problems of both unpressurised run-down of the turbine and then overheating of the bearing - hence the use of oil accumulator systems to maintain oil flow and cooling on these types of engines, and the advice to immediately re-start.

By the way, automotive turbos don't run at 2 to 3 times engine rpm - they typically run at around 100,000 rpm (no, that's not a misprint) at full load.

What doesn't disappear instantly when you slow down after highway running is the heat accumulated in the manifold, the exhaust turbine housing (which could be running at over 600C), the bearing housing and the compressor housing (even the compressor side could be running at over 150C at full boost). This mass of metal will not cool down very quickly, although a long coast down from highway speed reduces the temps markedly.

The means of removing this heat are a) 'cool' gas flow, b) oil flow through the bearing [and, if fitted, coolant flow through the bearing housing water jackets] - but all of these cease when the engine is stopped. So, the heat from the larger, hotter components flows into the smaller, cooler bearing housing and can easily heat the remaining oil well beyond it's breakdown point of, say, around 130-140C? (even if it's a u-beaut synthetic) - leading to 'coking' of the oil.

So, the advice to leave switching-off until the last moment after getting 'organised', etc. is sound. But I find the turbo-timer our vehicle had when we bought it second-hand is very convenient, so I use it often. I set it's cool-down period based on the EGT when we come to a standstill. After a bit of experience I known, for example, that it will take at least 4 minutes of idling after pulling up to drop the EGT to an acceptable level if it's still well over 300C at pull-up. This is not meant as a plug for EGT gauges but it is nice to be able to make the decision based on measurable fact rather then supposition or urban myth.

Hope this is found useful.
Ian

Hi Ian

Good read I will agree to most of your comments, as an ex earthmoving fitter not a light duty fitter I may be wrong!!!

This is Quoted out of my Toyota Troopy manual

Precautions for turning off an engine with a turbocharger
(1HD-FTE engine)
After high-speed or extended driving, etc., requiring a heavy engine load, the engine should be allowed to idle, as shown in the chart, before turning off.

Driving condition and required idling time

Normal city driving
Idling time -Not necessary

High-speed driving
About 80 km/h (50 mph)
idling time-About 20 seconds
About 100 km/h (63 mph)
Idling time-About 1 Minute

Steep mountain slopes or continued driving above 100 km/h (63 mph)
Idling time-About 2 minutes

Notice:
Do not turn the engine off immediately after a heavy load has been placed on the engine in order to prevent engine damage.

I've seen a lot of droopy exhaust valves because of heat on vee engines

Also have fitted some Pyrometer's in my time but have never seen 600 oC even on 500 hp engine.

maybe we weren't trying

But as I said before "it's alway a good thing to heat up an engine as wall as cool down an engine" (diesel, petrol,whatever fuel)

Regards

Richard

Hi Richard,

I appreciate your comments. The Troopy manual figures sound pretty good to me. I run longer cool-down times because a) the timer makes it easy to, and b) I think the cooler, the better, before switching off.

Regarding "Also have fitted some Pyrometer's in my time but have never seen 600 oC even on 500 hp engine. maybe we weren't trying": I'm guessing most, if not all, your pyros were fitted downstream of the turbo? The max. downstream temperatures will be a lot lower than the upstream ones (that's what I was quoting).

Some authorative US websites list upstream/downstream differences of 300F (~167 C) but I've actually measured almost 190 C difference in my vehicle. So, if it was 700 C upstream, it would be only about 510 C downstream.

This sounds like a very big difference, I know, but that's why turbo-charging is so effective - it extracts that much energy from the exhaust gas and uses it to compress the inlet air (up to 1.0bar (~15psig) in my case).

But it's the upstream temperature (or higher) that the piston crowns and exhaust valves are being subjected, and which the exhaust gas turbine blade tips, turbine housing and wastegate valve have to contend. I can't really understand why engine manufacturers continue to install only downstream of the turbo. All I can think is, that it's easier to put the probe into the turbo outlet pipe through a welded boss than to drill and tap into the manifold?

And perhaps some lingering concern that the probe might fail mechanically and fall into the turbine (although steam turbine manufacturers don't seem to feel the same concerns - turbine steam temperature thermocouples are common. And the consequences of falling into the blades are much more serious - by a factor of many $$$). A good quality thermocouple, properly fitted, will be extremely unlikely to fail in a catestrophic mechanical way. Even if subject to damaging vibration due to poor specification or fitting, it's much more likely it will fail internally and stop working long before it would mechanically 'break'.

I have quite a bit of experience with measurement and instrumentation in many heavy industrial situations and I have done some formal study and quite a lot of practical research into automotive turbo-diesel applications but I have no hands-on experience with heavy equipment, so I value the input from those that have real experience in these areas.

Ian

Hi Ian

I would have thought that the energy used to turn the turbine was Kinetic energy, not thermal energy.
I do understand that the expansion of the exhaust gases due to heat will give greater rate of flow across the turbine increasing it's speed and develop more pressure at the compressor wheel.
But the same could be achieved by cold air (exhaust) flow couldn't it?

As we can not create nor destroy energy but only change it to one form or another, how can we get thermal energy to turn a turbo?
Unless we changed it.

The ÄT is a result of movement e.g. flow (wind) heat has only one duty in life and that is to cool down.
As in hydraulics to have flow we must have a pressure drop.

I do understand that the internals of the engine do run hotter than the outside but, you must have faith in the design engineers as they do it for a living (much the same as you).

But to say that "Heat has everything to do with it" is only a small part of it the same as me saying that "Heats got F all to do with if."

As I said before "but it's alway a good thing to heat up an engine as wall as cool down an engine"

And follow the machine manufactures guild lines

Regards

Richard

ps it's been a good read

Richard and Ian, I have been watching your posts with interest. I must say the turboed agricultural gear I see doesn't have turbos much bigger than the ones like in Moses. Have a few 100 hp plus turbos here in John Deeres and also on the Cummins back up generator and nothing particularly large like earth movers or bigger trucks. Different to the superchargers entirely.

I was aware that if no airflow through the intercooler is no use, indeed it is worse than no use, it is to the detriment to performance as it reduces the pressure I believe because of the friction. I understand an intercooler can normally be expected to reduce the pressures by about 2-3 psi on the engine side! Hence a need to lift them more to overcome the intercooler. A 7 psi boost before the intercooler to a 2-3 drop to 4-5 psi post intercooler, even if a cooler hopefully more dense air intake. I think I need a higher pre intercooler boost.

Ian I understood it was exhaust gas FLOW that ran the turbo and compressed the air on the inlet side, rather than heat, which needs to be dissapated.

I can imagine a turbo will run down very quickly with no further gas going through it either side - exhaust or compression. I take the point Ian on the heat though. Another reason why I would love to get a 3" exhaust. ;-)

Richard, I wonder if there is enough room under the bonnet of modern 4bys to have an oven fitted up for harnessing the waste heat. Imagine get out of your 4by accross the Simpson, well perhaps just an inter camp run, to a roast chicken dinner at the end of the day. Perhaps we need an after cab box with an air intake past the turbo to do it.

Hi Richard and John,

Indeed an interesting discussion. My apologies to Coyote - we seem to have thoroughly hi-jacked your original thread about turbo timers - but it's all good stuff, no?

Let me say again, I make no claims to be an expert on engine and turbo-charger design - my experience is in instrumentation and control systems. But I did study (and pass! - strangely enough) units in thermodynamics & thermo-fluid mechanics, albeit many moons ago now. So, while I think the following is fairly accurate, I'll happily stand corrected if some (or all!) of this is wrong:

As I understand it, there are two basic types of turbine, impulse and reaction. The difference is easier to understand if you think of hydro-electric (water) turbines.

Impulse turbines, such as Pelton Wheels, rely on relatively low flow rates but high pressure water (say, several hundreds of metres of 'head' pressure) to create a jet of very high velocity water (ie. lots of kinetic energy) which impacts upon the turbine blades (more like little buckets really) and the kinetic energy is converted into mechanical energy in the turbine shaft. The 'exhaust' water has no pressure and low velocity.

Reaction turbines, such as Francis turbines used in many low-speed vertical shaft hydro generators, use large flow rates and relatively low pressure (head). They rely on the 'reaction' of water flow over the turbine blades, in the same way an aeroplane wing creates lift.

With gas turbines it gets a bit messier, as gases expand and contract and change in temperature, while water (in general) does not. Power generation steam turbines use, AFAIK, a combination of impulse and reaction turbine blade designs. IIRC, the first few blade stages are primarily impulse blades to take advantage of the velocity (kinetic energy) of the steam emerging from the throttle jets, while the majority of the stages are reaction blades, using the flow of the expanding (and cooling!) steam to convert thermal energy into mechanical energy.

I believe turbo-charger exhaust gas turbines are reaction turbines. Therefore, as you both say, it is gas FLOW over the turbines blades that produces the mechanical energy to drive the compressor side. And that the gas will only flow if there is a pressure difference between the inlet and outlet sides of the turbine to create the flow. BUT, it's a basic law of physics that if you lower the pressure of any gas, it gets cooler [and vice-versa, if you increase it's pressure it gets hotter] (- after all, this is the fundamental principle that makes diesel engines work in the first place).

So the gas coming out of a turbine must be lower in pressure AND temperature than what went in, otherwise you've not extracted any energy from it and the turbine can't develop any power.

As an aside to back this up, AFAIK, all power generation steam turbines of any real size (say, >60MW) use superheaters and RE-HEAT. The steam comes from the boiler's superheater stage, where it's deliberately heated to temperatures well above the boiling point at whatever is the operating pressure, and is expanded across the first turbine stage (HP - high pressure). Then the steam flows back to the boiler and is re-heated to a higher temperature again before being expanded through the MP and LP turbine stages. The steam pressure doesn't increase during re-heat (it can't, otherwise the flow would start to go backwards!) - only the temperature.

At the exhaust of the LP stage, the pressure is kept at nearly full vacuum (about -100kPag) and the temperature is below 100C. The object is to have the steam going into each turbine stage at the highest practical pressure AND TEMPERATURE and have it coming out at the lowest pressure AND TEMPERATURE (but still in the gaseous phase). This gives the maximum possible power output and efficiency.

Back to automotive turbos: Richard, I don't think I'm doubting the abilities of the design engineers by questioning the placement of EGT sensors. It is an undeniable and easily measured fact that there is a large temperature drop across a turbo-charger's exhaust gas turbine at high loads. Engine designers are quite able to quantify the difference for any particular 'standard' engine design and specify an appropriate 'downstream' limit in their operating instructions.

Many of my customers are quite happy with their downstream measurement. But I maintain it is inherently better to measure the upstream temperature directly, rather than infer when it might be too high based on the downstream temperature and an assumed maximum difference. More so for any 'non-standard' engine ('chipped', non-standard pump settings, aftermarket turbo, etc.), as more unknown variables come into the mix.

I agree that "Heat has everything to do with it" is over simplistic. And that warm up and cool down are both important. And that, in general, the manufacturers guidelines should be followed. [But then, few of us do this religiously. Anyone with any non-standard part or accessory on their vehicle is not following the guideline I've seen in every owner's handbook I've ever seen: "Fit and use only genuine xxxxxx parts and accessories"...]

John, not sure exactly what your point is about intercooler pressures? While I've not measured it myself, I be surprised if a clean, original 4WD vehicle intercooler had a drop of 3 psi as standard. However, if you're concerned about too much pressure drop across it (and assuming it's not clogged or excessively fouled internally) a simple way to overcome the pressure drop in non-electronically controlled engines, is to move the pressure sensing point from the compressor outlet port (where is usually is as standard) to a tapping off the actual inlet manifold. Then the wastegate will be operating to maintain constant manifold pressure rather than constant compressor outlet pressure.

The small hose from the compressor outlet to the wastegate will usually have a tee-off going to the injection pump's pressure compensator. Make sure this is moved to the new tapping point too and remember to plug the compressor port.

Eagerly await the next instalment(s). Maybe we should start a new thread - Turbo Talk????

Ian, sorry if I am not making myself plain on issues, this is waaay off my area of study but very interesting. The point I am making is that the cooler air from the intercooler being more dense is good for the engine as it gets more into the cylinder. Doesn't that assume the pressure it goes in at is the same as the warmer air?

I was told by one of the engineering folk at MTQ Engine Systems, Laverton that the restriction through the intercooler caused that sort of pressure drop. It seemed to me you should seek more to compensate for such a drop. Perhaps such a density may be too high for the motor, but I would have though that doubtful.

I reckon the turbo talk idea is good too Ian, also about the bl**dy EGR valve and as to wether that is useful or not!!!! The smog I get here is from the gas processing from the gas fields to the South......

Hi Ian
Pressure is the sum of resistance to flow of a liquid (fluid or gas) the pressure build up before the turbine is due to the resistance to flow and equal to the amount of energy to drive the compressor wheel and tail pipe, I would say.

The steam you talk about does not flow back wards (Maybe because of check valves) if you heat a liquid it will expand, if it can't the pressure will increase (laws of physics) eg Boyle, Charles, Gay-Lussac)

I do under stand that the speed of the turbo is directly related to the temperature of the exhaust gas and its rate of expansion as it travel through it, but this is the energy that is being used speed (velocity, kinetic energy) not thermal. these are only my opinion and I don't mined being wrong, as it means Ive learned something new for today..

Regards

Richard

Hi Richard & John,

Richard, looks like we may have to agree to disagree. But a couple of parting shots...

About the steam turbines - no, there are no check valves, just a steadily dropping pressure from highest pressure part of the system (the feedwater pumps) through the boiler water drum, the superheater, the HP turbine stage, the re-heater, the MP and LP turbine stages to the condenser, which is well below atmospheric pressure, as mentioned. I don't know which of the illustrious gentlemen you mentioned came up with it but one of the fundamentals of thermodynamics is the Ideal Gas Equation: (PxV)/T = Constant [P=pressure, V=volume, T=temperature].

So, as you say, when we re-heat the steam it does expand but the pressure does not rise if the volume also is allowed to increase. This is what happens: after re-heat, the same mass of steam exists but it occupies greater volume. In this case of a dynamic flowing system, the same mass flow of steam (kg/sec) will, as you say, expand (more m3/sec) and need to travel faster through the pipes (higher velocity in m/sec). And therefore be able to deliver more energy to the MP and LP turbines. Because more energy was put into the steam by raising it's temperature.

And just one last point: why do you reckon the science of this stuff is called THERMOdymanics, if heat has so little to do with it?

John,
Indeed, the whole point of intercooling (charge cooling) is to increase the air charge density so that you end up with a great MASS of air in the cylinders. It's the exact opposite of what I was waffling about above, with steam re-heat. Reduce the temperature and the volume occupied by the same mass of air reduces and therefore it's density increases.

But, as you say, to get the full advantage of charge cooling, you do need the actual manifold pressure to be maintained - hence my suggestion to sense the pressure at the manifold, rather than at the compressor outlet. I can't see this causing a problem provided you don’t actually adjust the wastegate to raise the pressure setting.

The pressure drop across the cooler will increase with flow rate. Therefore at lower revs (but sufficient to develop full boost , say 2000 rpm) there might be quite a low pressure drop and near full boost pressure at the manifold. However, at 4000 rpm the drop will be quite a lot higher and quite a bit less manifold pressure. Moving the sensing point just allows the full 'standard' pressure to be maintained at the manifold regardless of flow rate (rpm).

Might make this my last post on this thread.

Ian

Don't give up

The illustrious gentlemen I mentioned came up with it but one of the fundamentals of thermodynamics is the Ideal Gas Equation: (PxV)/T = Constant [P=pressure, V=volume, T=temperature].
They wrote the LAW. and it's a combination of them

It's pV over T = constant or p1.V1 over T1 = p2.V2 over T2

Please tall me, if you put a Turbo up against a heat source would it spin?

I would think not.

You cannot compare a steam turbine with a IC engine Turbo as the IC engine uses the waste energy of the exhaust to run it's self (free energy).
The steam turbine has to have heat the covert the liquid to steam (vapor) to run with it< James would not have had anything to sell......

Pulled from the net

The First Law of ThermodynamicsToward the middle of the 19th cent. heat was recognized as a form of energy associated with the motion of the molecules of a body (see kinetic-molecular theory of gases kinetic-molecular theory of gases, physical theory that explains the behavior of gases on the basis of the following assumptions: (1) Any gas is composed of a very large number of very tiny particles called molecules; (2) The molecules are very far apart compared to their sizes, so that they can be considered as points; (3) The molecules exert no forces on one another except during rare collisions, and these collisions are perfectly elastic, i.
. Speaking more strictly, heat refers only to energy that is being transferred from one body to another. The total energy a body contains as a result of the positions and motions of its molecules is called its internal energy; in general, a body's temperature temperature, measure of the relative warmth or coolness of an object. Temperature is measured by means of a thermometer or other instrument having a scale calibrated in units called degrees. The size of a degree depends on the particular temperature scale being used. A temperature scale is determined by choosing two reference temperatures and dividing the temperature difference between these two points into a certain number of degrees.
is a direct measure of its internal energy. All bodies can increase their internal energies by absorbing heat (see heat capacity). However, mechanical work done on a body can also increase its internal energy; e.g., the internal energy of a gas increases when the gas is compressed. Conversely, internal energy can be converted into mechanical energy; e.g., when a gas expands it does work on the external environment. In general, the change in a body's internal energy is equal to the heat absorbed from the environment minus the work done on the environment. This statement constitutes the first law of thermodynamics, which is a general form of the law of conservation of energy (see conservation laws conservation laws, in physics, basic laws that together determine which processes can or cannot occur in nature; each law maintains that the total value of the quantity governed by that law, e.g., mass or energy, remains unchanged during physical processes. Conservation laws have the broadest possible application of all laws in physics and are thus considered by many scientists to be the most fundamental laws in nature.

The Second Law of ThermodynamicsA cyclic process is one that returns the system, but not the environment, to its original state. A closed cycle consisting of two isothermal and two adiabatic transformations is called a

Carnot cycle after the French physicist Sadi Carnot Carnot, Sadi (sädç` kärnô`), 1837–94, French statesman, president of the Third Republic (1887–94); son of Hippolyte Carnot.
who first discussed the implications of such cycles. During the Carnot cycle occurring in the operation of a heat engine, a definite quantity of heat is absorbed from a reservoir at high temperature; part of this heat is converted into useful work, but the balance is expelled into a low-temperature reservoir and thus "wasted." The greater the temperature difference between the two reservoirs, which in a steam engine are represented by the boiler and the condenser, the greater the fraction of absorbed heat that is converted into useful work. It is, however, theoretically impossible to convert all the heat extracted from the reservoir into useful work.

In general it is impossible to perform a transformation whose only final result is to convert into useful work heat extracted from a source that is at the same temperature throughout. This statement is Lord Kelvin's version of the second law of thermodynamics. Another version of this law, formulated by R. J. E. Clausius, states that a transformation is impossible whose only final result is to transfer heat from a body at a given temperature to a body at higher temperature; in other words, the spontaneous flow of heat from hot to cold bodies is reversible only with the expenditure of mechanical or other nonthermal energy. These two versions of the second law of thermodynamics can be shown to be entirely equivalent.

The second law is expressed mathematically in terms of the concept of entropy entropy (ĕn`trəpç), quantity specifying the amount of disorder or randomness in a system bearing energy or information. Originally defined in thermodynamics in terms of heat and temperature, entropy indicates the degree to which a given quantity of thermal energy is available for doing useful work—the greater the entropy, the less available the energy.
When a body absorbs an amount of heat Q from a reservoir at temperature T, the body gains and the reservoir loses an amount of entropy S=Q/T. Thus, in a reversible adiabatic process (no heat change) there is no change in the total entropy. If an amount of heat Q flows from a hot to a cold body, the total entropy increases; because S=Q/T is larger for smaller values of T, the cold body gains more entropy than the hot body loses. The statement that heat never flows from a cold to a hot body can be generalized by saying that in no spontaneous process does the total entropy decrease.

In all real physical processes entropy increases; in ideal reversible processes entropy remains constant. Thus, in the Carnot cycle, which is reversible, there is no change in the total entropy. The engine itself experiences no net change in entropy because it is returned to its original state at the end of the cycle. The entropy gained by the low temperature reservoir is equal to the entropy lost by the high temperature reservoir. However, according to the formula S=Q/T, less heat need be expelled into the low temperature reservoir than is extracted from the high temperature reservoir for equal and opposite changes in entropy. In the Carnot cycle this difference in heat appears as useful mechanical work.

The Third Law of ThermodynamicsA postulate related to but independent of the second law is that it is impossible to cool a body to absolute zero by any finite process. Although one can approach absolute zero as closely as one desires, one cannot actually reach this limit. The third law of thermodynamics, formulated by Walter Nernst and also known as the Nernst heat theorem, states that if one could reach absolute zero, all bodies would have the same entropy. In other words, a body at absolute zero could exist in only one possible state, which would possess a definite energy, called the zero-point energy. This state is defined as having zero entropy.

No need to reply

I'm not trying to win anything

And i'm not having SHOTS

Regards

Richard

Richard,
You said "don't give up", so... Sorry if my flippant remark about "passing shots" gave offence - it was not intended to.

OK, we seem to agree about the existence and form of the Ideal Gas Equation and/or LAW. And the various laws of thermodynamics.

"Please tall me, if you put a Turbo up against a heat source would it spin?" Sorry, don't see the point of the question. I've never suggested any remotely like this.

Thanks for digging out all the thermodynamic theory. I fully confirms what I've been trying to say in less scientific terms. Notice statements such as: "heat was recognized as a form of energy ", "in general, a body's temperature... is a direct measure of its internal energy." and "Conversely, internal energy can be converted into mechanical energy". Do these not confirm what I've been saying: the difference in the inlet and outlet temperatures of the exhaust gas through a turbo is directly related to the energy put into driving the compressor wheel.

Regarding your statements: "You cannot compare a steam turbine with a IC engine Turbo as the IC engine uses the waste energy of the exhaust to run it's self (free energy).
The steam turbine has to have heat the covert the liquid to steam (vapor) to run with it< James would not have had anything to sell...... ":
Yes, you certainly compare a steam turbine with a turbo's exhaust gas turbine. They are both gas turbines and their principles of operation are identical. It makes no difference to the operation of the turbine what it's source of hot high pressure gas is, or whether you regard it as 'free' or not.

A turbo would behave very similarly if fed with steam at the same temperature and pressure as the exhaust from an IC engine. [please note, I say "behave very similarly" not "identically" because there would be some differences related to the different density and heat capaciity of the two different gases. But not due to any differences in operating principles.]

Again, from your own sources: "During the Carnot cycle occurring in the operation of a heat engine, a definite quantity of heat is absorbed from a reservoir at high temperature; part of this heat is converted into useful work, but the balance is expelled into a low-temperature reservoir and thus "wasted"." and "The greater the temperature difference between the two reservoirs, which in a steam engine are represented by the boiler and the condenser, the greater the fraction of absorbed heat that is converted into useful work."

The second sentence could just as well read "The greater the temperature difference between the two reservoirs, which in an exhaust gas turbine are represented by the IC engine exhaust gas manifold and the turbo dump pipe, the greater the fraction of absorbed heat that is converted into useful work.", and be equally correct.

If I've interpreted your information wrongly, I'd be happy to be corrected - but I don't think anything I've proposed goes against the thermodynamics information you've presented - rather it's completely in agreement with it.
Ian

Hi Justin,

Just a couple of points:

. "In nearly every other situation, the turbo has cooled down by the time it takes to park the car, find the wallet and all that other stuff." - how do you know it has cooled down? And what is 'cool'?

. I've found the transmission brake to be rock solid on both my old Series III ute and our '97 Disco. Id' much rather have one of these than any type of rear wheel park brake.

Hi Ken,

. "modern turbo's have water cooled bearings" - not necessarily, there's plenty of non-water cooled ones about. For example, the Nissan TD42T engine (GU Patrol) has water cooled turbo bearings but the newer TD42Ti (intercooled) engine (GU Patrol TD6) does not.

. "and low inertia turbine wheels, they slow down [and speed up] and cool off quickly" - low inertia, quick slow down and speed up - I agree wholeheartedly. "cool off quickly" - sorry, must disagree. Please have a look at my Follow-up two posts earlier. I'd appreciate you comments.

Ian

Hi Ian , my grammer was a bit wrong I did not mean cool off time to be associated with the speed, All you say about heat soak into the bearing I agree with. I find however these days automotive turbos are very reliable regardless of how they are treated and most seem to be good for300,000 or better, agricultural applications are another matter.
On the subject of TD42 TI Nissan I see that they have an EGR valve now with a water jacket and coolant pipes any theories on this? I know why the EGR is there Ijust have never seen a water cooled one before. It has cairtainly not improved the accesability of the oil filters.
Regards Ken.

Hi Ken,

The dreaded EGR (Exhaust Gas Recirculation) - never been able to work out the logic of meself.

The theory goes: very high combustion temperatures cause nitrogen and oxygen in the combustion air to combine to form oxides of nitrogen (I think the bad ones are NO & NO2,). Whichever ones, these are the major culprits in forming photo-chemical smog in large cities, so the powers that be have declared that vehicles must put out less than a certain % of oxides of nitrogen to meet emission standards. And the method they use: dilute the combustion air charge to the engine by mixing some of the exhaust gases back into the inlet system under certain conditions (generally heavy load conditions).

The result: combustion temperatures are reduced because the effective percentage of oxygen in the combustion 'air' is now less than the
'natural' level of about 21% - and a lower PERCENTAGE of oxides of nitrogen is present in the exhaust gas. BUT, I've never been able to reconcile the fact that EGR, by it's very nature, reduces the operating efficiency of the engine and therefore, the engine must use more fuel (and overall, produce more exhaust products) to accomplish the same job!

It's always seemed to me to be a bit self-defeating. I mean, the manufacturers use turbo-charging, high-pressure, extremely finely atomised injection systems and precise electronic controls on injection timing and duration to get the maximum possible efficiency out of modern diesels - than slap on EGR to undermine their best efforts??

Getting a bit off-thread here - back to you question about the TD42Ti Nissan engine. From the horses mouth (Nissan technical bulletin):

"EGR (Exhaust Gas Recirculation) has been adopted to the TD42Ti. EGR is added to improve emission performance, ie; lower the NOx emissions.
The EGR lowers engine combustion temperatures which has the added benefit of reducing the NOx emissions.
In the case of the TD42Ti part of the EGR piping is a water cooled unit."

and

"To assist in maintaining lower combustion temperatures, the exhaust gas that is recirculated back into the engine via the EGR system is further lowered in temperature by an EGR cooler." [and more unnecessary load on the cooling system??]

Now, far be it from me to suggest anyone remove such an important anti-emissions device, but that EGR cooler looks like it could be easily converted into a nice camping shower hot water heater...

One last point: should anyone remove the EGR system (for, say, off-road competition??), be aware that your full load combustion temperatures will rise, as will the maximum exhaust gas temperature [EGT] - simply because you are now burning your fuel in 'real' air.

Ian