Gas vs PSD
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From: Long Island USA
I've heard that "waste heat" argument about turbos before, and had a long drawn-out debate with someone on this site about it.
The turbo doesn't directly use heat to generate boost. There is a VERY slight difference in heat before and after the turbo, because of the difference in actual pressure in the exhaust before and after the turbo. Much like a propane cylinder will get cold as you allow gas to escape, the exhaust temp drops after the turbo for much the same reason. Lowering the pressure of any gas will drop it's temperature. Likewise, keeping the temperature UP before the turbo helps boost, because pressure is higher before turbo, increasing power.
But "heat" in and of itself is not "consumed" by the turbo to generate boost.
But this is the V10 vs. PSD thread
The turbo doesn't directly use heat to generate boost. There is a VERY slight difference in heat before and after the turbo, because of the difference in actual pressure in the exhaust before and after the turbo. Much like a propane cylinder will get cold as you allow gas to escape, the exhaust temp drops after the turbo for much the same reason. Lowering the pressure of any gas will drop it's temperature. Likewise, keeping the temperature UP before the turbo helps boost, because pressure is higher before turbo, increasing power.
But "heat" in and of itself is not "consumed" by the turbo to generate boost.
But this is the V10 vs. PSD thread
Lead Driver
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You have got some good posts in this thread 
why thank you.
A part of the reason that you haven't seen a turbo gas engine that is more efficient than a NA diesel is the way in which they were built into the engine's architecture. Turbo's have typically been bolted on to gas engines in the pursuit of more power for a given engine/size/weight, and the turbo's have been sized and put on engines to get more power up in the higher rpm range. Turbo's were seen by the general public as a hi-po power adder to gas engines, and were typically fitted only to vehicles that fitted that purpose.
while this is true, any diesel from the factory generally has a fitted turbo for a very modest power level (maximizing mileage), it doesnt mean that the turbo is the reason they are efficient. cuz its not. . .the turbo basically makes an already more efficient setup, more efficient. the thermal efficiency of an NA diesel vs an NA gasser tells the whole story, the diesel is still 30-40% more efficient.
Improvements in technology and the general public crying out for better gas milage on their everyday vehicles has meant that some turbo gas engines are getting damn close to their diesel brethren in gas milage.
Volkswagen's TSI engine (1.4l I4, turbo-charged with a positive displacement blower as well to provide boost at low rpms) gets milage close to their similar powered 2.0l TDI.
I would anticipate the next wave of Ford's ecoBoost engines to perform similarly, their 1.0l 3cyl turbo which will provide similar power to their 1.6 TDCI, and probably provide similar milage.
i admitted/acknowledge the efficiency gap was closing thanks to technology. with the introduction of direct injection being the most proficient design enhancing performance/efficiency, manufacturers are finding ways to use the same technology that makes diesels so great. BUT, just as i said, the gap can only be closed so far. the injection pressures and compression ratio cannot be raised to diesel levels with current technology. and those who have gone above and beyond to make the most efficient gassers, still fell short of the thermal efficiency of a compression ignition diesel.
All in all, in a perfect world, a diesel engine will be more "efficient" per say, but a number of gas engines that have been build with "milage" specifically in mind are closing the gap on real world fuel efficiency.
the technology being applied to gassers today, like the ecoboost, have been around for decades. the cry for good mileage (which has been going on since the '70's) couldnt propel technology to make reliable systems until now. and, their reliability is still yet to be determined. turbo'd direct injected gasoline motors in production now are still missing 3 things needed to get a thermal efficiency rating "as close as possible" to that of the current diesels in place.
1) higher injection pressures: gasoline wont need identical pressures as the diesel (since gasoline atomizes partly on its own), but 400 psi to gasoline is nothin compared to 36,000+ psi of diesel
2) compression ratio: even the prototype compression ignition gasoline motors still are limited to 14-14.5:1. this i dont think will ever change, gasoline is just too volatile to be used in anything higher, especially if one expects to add a turbocharger to the equation (would be very difficult at this level of compression)
3) this is sorta related to 2. . .because the compression ratio cannot match that of a diesel, nor can match its ability to make incredible low end hp.
-all in all the volatility makes it impossible to have a gasser that "has the best of all worlds" like the diesel. diesel fuel, being so hard to ignite, can be subjected to the incredible conditions that make the motors they fuel so much more efficient. i.e. A/F ratio doesnt matter, timing matters much less, as does compression ratio.
why thank you.
A part of the reason that you haven't seen a turbo gas engine that is more efficient than a NA diesel is the way in which they were built into the engine's architecture. Turbo's have typically been bolted on to gas engines in the pursuit of more power for a given engine/size/weight, and the turbo's have been sized and put on engines to get more power up in the higher rpm range. Turbo's were seen by the general public as a hi-po power adder to gas engines, and were typically fitted only to vehicles that fitted that purpose.
while this is true, any diesel from the factory generally has a fitted turbo for a very modest power level (maximizing mileage), it doesnt mean that the turbo is the reason they are efficient. cuz its not. . .the turbo basically makes an already more efficient setup, more efficient. the thermal efficiency of an NA diesel vs an NA gasser tells the whole story, the diesel is still 30-40% more efficient.
Improvements in technology and the general public crying out for better gas milage on their everyday vehicles has meant that some turbo gas engines are getting damn close to their diesel brethren in gas milage.
Volkswagen's TSI engine (1.4l I4, turbo-charged with a positive displacement blower as well to provide boost at low rpms) gets milage close to their similar powered 2.0l TDI.
I would anticipate the next wave of Ford's ecoBoost engines to perform similarly, their 1.0l 3cyl turbo which will provide similar power to their 1.6 TDCI, and probably provide similar milage.
i admitted/acknowledge the efficiency gap was closing thanks to technology. with the introduction of direct injection being the most proficient design enhancing performance/efficiency, manufacturers are finding ways to use the same technology that makes diesels so great. BUT, just as i said, the gap can only be closed so far. the injection pressures and compression ratio cannot be raised to diesel levels with current technology. and those who have gone above and beyond to make the most efficient gassers, still fell short of the thermal efficiency of a compression ignition diesel.
All in all, in a perfect world, a diesel engine will be more "efficient" per say, but a number of gas engines that have been build with "milage" specifically in mind are closing the gap on real world fuel efficiency.
the technology being applied to gassers today, like the ecoboost, have been around for decades. the cry for good mileage (which has been going on since the '70's) couldnt propel technology to make reliable systems until now. and, their reliability is still yet to be determined. turbo'd direct injected gasoline motors in production now are still missing 3 things needed to get a thermal efficiency rating "as close as possible" to that of the current diesels in place.
1) higher injection pressures: gasoline wont need identical pressures as the diesel (since gasoline atomizes partly on its own), but 400 psi to gasoline is nothin compared to 36,000+ psi of diesel
2) compression ratio: even the prototype compression ignition gasoline motors still are limited to 14-14.5:1. this i dont think will ever change, gasoline is just too volatile to be used in anything higher, especially if one expects to add a turbocharger to the equation (would be very difficult at this level of compression)
3) this is sorta related to 2. . .because the compression ratio cannot match that of a diesel, nor can match its ability to make incredible low end hp.
-all in all the volatility makes it impossible to have a gasser that "has the best of all worlds" like the diesel. diesel fuel, being so hard to ignite, can be subjected to the incredible conditions that make the motors they fuel so much more efficient. i.e. A/F ratio doesnt matter, timing matters much less, as does compression ratio.
FTE Leadership Emeritus
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From: Melbourne, Aus
In longer version - using the propane analogy you used.
Temperature and Pressure are directly related (PV=nRT). In order to hold Propane under such pressure, it is cooled to being liquid form - the reason that the cylinder gets cold is not due to the pressure change, it is due to the temperature change (to get pedantic, the pressure change allows the temperature to change, but it is the temperature chance that is the cause...). The liquid now needs to heat up to transition to a gaseous state, rapidly, and requires thermal energy to do so - which it draws from the much warmer propane cylinder and its surrounding air.
In the case of a turbo.
The turbo converts the pressure, which is generated by the exhaust temperature.
Lead Driver
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I've heard that "waste heat" argument about turbos before, and had a long drawn-out debate with someone on this site about it.
The turbo doesn't directly use heat to generate boost. There is a VERY slight difference in heat before and after the turbo, because of the difference in actual pressure in the exhaust before and after the turbo. Much like a propane cylinder will get cold as you allow gas to escape, the exhaust temp drops after the turbo for much the same reason. Lowering the pressure of any gas will drop it's temperature. Likewise, keeping the temperature UP before the turbo helps boost, because pressure is higher before turbo, increasing power.
But "heat" in and of itself is not "consumed" by the turbo to generate boost.
But this is the V10 vs. PSD thread
The turbo doesn't directly use heat to generate boost. There is a VERY slight difference in heat before and after the turbo, because of the difference in actual pressure in the exhaust before and after the turbo. Much like a propane cylinder will get cold as you allow gas to escape, the exhaust temp drops after the turbo for much the same reason. Lowering the pressure of any gas will drop it's temperature. Likewise, keeping the temperature UP before the turbo helps boost, because pressure is higher before turbo, increasing power.
But "heat" in and of itself is not "consumed" by the turbo to generate boost.
But this is the V10 vs. PSD thread
just like the other guy said: yes it is. . .
"in long" :
"energy cannot be created nor destroyed, it can only change forms". the heat expelled from a motor is complete and utter wasted energy. heat that comes off your transmission, axle, etc is all wasted energy (friction). some of the heat generated by combustion is translated into mechanical motion (pistons, crank, etc) which propels the truck. "thermal efficiency" is a rating of how much of this heat (energy) from the combustion is converted to work. anything that uses heat from the combustion is using the energy the combustion provides. . .the turbo is just another way of harnessing the exhaust gasses/heat (wasted energy) in order to utilize as much of the available heat from the combustion as possible. . .TURBOS COULD NOT INCREASE THERMAL EFFICIENCY IF THEY DIDNT USE HEAT FROM THE COMBUSTION TO OPERATE (not yelling, bein lazy with bolds)
why is there a temp difference before/aft the turbo? BECAUSE THE HEAT WAS CONVERTED INTO MECHANICAL MOTION (SPINNING OF TURBO WHEELS) AND THE TURBO SOAKED UP SOME OF THE WASTED ENERGY. . .RESULTING IN A TEMP DECREASE (LESS ENERGY GOING OUT VS WHAT WAS GOING IN).
as far as the cummins swap, should i pm the guy all of my suggestions about possible options to save him time and money with his truck? that way i can keep it outta the thread?
Senior User
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I have seen folks with pyros documenting heat loss post-turbo, but its due to the compression of the air pre-turbo more than the turbo consuming heat (there is a physics of thermal transfer, that I can't explain). The 6.0L sees maybe 700-800* cruising on the interstate, post turbo temps are anywhere from 50-200* cooler depending on how much boost is run.
Turbochargers aside, gassers will have their limits with natural aspiration. Ford is making huge progress in the Gassers, with the direct injection and the EcoBoost series engines. Which I see them taking and expanding to nearly all of their gassers in the coming years. A turbo would be a huge benefit to the V10, particularly a twin set-up similar to the EcoBoost.
Turbochargers aside, gassers will have their limits with natural aspiration. Ford is making huge progress in the Gassers, with the direct injection and the EcoBoost series engines. Which I see them taking and expanding to nearly all of their gassers in the coming years. A turbo would be a huge benefit to the V10, particularly a twin set-up similar to the EcoBoost.
Lead Driver
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yes, part of the heat indicated on a pyrometer that is pre turbo is generated by the compression of gasses inside the manifold (this is called drive pressure, the compression of gasses causes heat. . .i.e. compression ignition), however, it takes energy to compress the gasses. . .it comes from the pistons, which are being forced by the combustion of fuel. . . .the fuel can only offer its energy via heat. everything we are talkin about comes from the energy released in the form of heat via the combustion process. . . . .an internal combustion motor is merely a device used to harness heat energy.
the increase in EGT from the compression of gasses between the drive wheel of the turbo and the exhaust valves of the motor is minute compared to the initial temp of the gasses themselves. drive pressure of 30-40 psi (typical close to stock DP) is nothing compared to the xxx,xxx? psi/millisecond generated by the combustion where the heat source is being released.
the increase in EGT from the compression of gasses between the drive wheel of the turbo and the exhaust valves of the motor is minute compared to the initial temp of the gasses themselves. drive pressure of 30-40 psi (typical close to stock DP) is nothing compared to the xxx,xxx? psi/millisecond generated by the combustion where the heat source is being released.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Believe me, I've been through this before. It might be semantics, and I do understand what you are going to say. And what 89Fturd is saying.
It amounts to the amount of heat that comes out the tailpipe is lower on a turbo vehicle per HP compared to a non-turbo, so in effect, it's "thermal efficiency" is higher.
But that's kinda like saying my propane-powered barbecue MUST have a higher thermal efficiency than a natural-gas-powered one, because the propane tank gets cold while my natural gas pipeline doesn't.
The pressure differential in a turbo causes it to spin, and the heat "loss" is a by-product of pressure drop. The heat in and of itself doesn't cause the turbo to spin.
It amounts to the amount of heat that comes out the tailpipe is lower on a turbo vehicle per HP compared to a non-turbo, so in effect, it's "thermal efficiency" is higher.
But that's kinda like saying my propane-powered barbecue MUST have a higher thermal efficiency than a natural-gas-powered one, because the propane tank gets cold while my natural gas pipeline doesn't.
The pressure differential in a turbo causes it to spin, and the heat "loss" is a by-product of pressure drop. The heat in and of itself doesn't cause the turbo to spin.
Lead Driver
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Believe me, I've been through this before. It might be semantics, and I do understand what you are going to say. And what 89Fturd is saying.
It amounts to the amount of heat that comes out the tailpipe is lower on a turbo vehicle per HP compared to a non-turbo, so in effect, it's "thermal efficiency" is higher.
But that's kinda like saying my propane-powered barbecue MUST have a higher thermal efficiency than a natural-gas-powered one, because the propane tank gets cold while my natural gas pipeline doesn't.
The pressure differential in a turbo causes it to spin, and the heat "loss" is a by-product of pressure drop. The heat in and of itself doesn't cause the turbo to spin.
It amounts to the amount of heat that comes out the tailpipe is lower on a turbo vehicle per HP compared to a non-turbo, so in effect, it's "thermal efficiency" is higher.
But that's kinda like saying my propane-powered barbecue MUST have a higher thermal efficiency than a natural-gas-powered one, because the propane tank gets cold while my natural gas pipeline doesn't.
The pressure differential in a turbo causes it to spin, and the heat "loss" is a by-product of pressure drop. The heat in and of itself doesn't cause the turbo to spin.
its thermodynamics 101 i hate to say. heat energy drives the turbo.
the pressure differential is produced by the heat energy released by the combustion. . .even if what you say were true, and a turbo was solely driven off a pressure differential, the pressure would not be there if the thermal energy from the combustion didnt put it there. . .heat still causes the pressure differential you speak of. . . .everything takes energy to move. there is no energy source on any of our truck besides heat. the movement of the turbo is caused by heat. again, the thermal efficiency of the motor couldnt increase from a turbo if heat isnt what the turbo used in order to function. . .
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
No, it doesn't. There is HIGH pressure BEFORE the exhaust turbine. There is LOWER pressure AFTER the exhaust turbine, because the turbine is a restriction.
If you take any gas at a certain temperature, and lower it's pressure, it's temperature drops.
It's a cart-before-the-horse sort of thing. Which is it? That the turbo is directly using heat as a power source? Or that the turbo is a restriction in the exhaust flow, causing a pressure drop, causing lower temperatures after the turbo?
FTE Leadership Emeritus
Joined: May 2004
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From: Melbourne, Aus
Have a look at the nozzles for the burners for both bbq's. The Natural Gas ones will be probably twice as large in diameter
The efficiency of a bbq is independent of the pressure that its fuel is stored at
The pressure differential in a turbo causes it to spin, and the heat "loss" is a by-product of pressure drop. The heat in and of itself doesn't cause the turbo to spin.
FTE Leadership Emeritus
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From: Melbourne, Aus
I already posted, but I gotta answer this, because it's the root of the idea that the turbo "converts heat into mechanical motion".
No, it doesn't. There is HIGH pressure BEFORE the exhaust turbine. There is LOWER pressure AFTER the exhaust turbine, because the turbine is a restriction.
If you take any gas at a certain temperature, and lower it's pressure, it's temperature drops.
It's a cart-before-the-horse sort of thing. Which is it? That the turbo is directly using heat as a power source? Or that the turbo is a restriction in the exhaust flow, causing a pressure drop, causing lower temperatures after the turbo?
No, it doesn't. There is HIGH pressure BEFORE the exhaust turbine. There is LOWER pressure AFTER the exhaust turbine, because the turbine is a restriction.
If you take any gas at a certain temperature, and lower it's pressure, it's temperature drops.
It's a cart-before-the-horse sort of thing. Which is it? That the turbo is directly using heat as a power source? Or that the turbo is a restriction in the exhaust flow, causing a pressure drop, causing lower temperatures after the turbo?
If you take a N/A engine. The exhaust pressure is atmospheric - no energy. The temperature however... could be up to 1600F.
Where can you get the energy to drive the turbo from?
Lead Driver
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I already posted, but I gotta answer this, because it's the root of the idea that the turbo "converts heat into mechanical motion".
No, it doesn't. There is HIGH pressure BEFORE the exhaust turbine. There is LOWER pressure AFTER the exhaust turbine, because the turbine is a restriction.
the drive pressure couldnt be there without the heat of the combustion. . .the turbo is run off heat energy theres no way you can put it to disprove the physics behind this.
If you take any gas at a certain temperature, and lower it's pressure, it's temperature drops.
It's a cart-before-the-horse sort of thing. Which is it? That the turbo is directly using heat as a power source? Or that the turbo is a restriction in the exhaust flow, causing a pressure drop, causing lower temperatures after the turbo? the pressure variation wouldnt be there without energy to make it so (a pressure variation requires energy)! heat is the only source of energy!!!!!
No, it doesn't. There is HIGH pressure BEFORE the exhaust turbine. There is LOWER pressure AFTER the exhaust turbine, because the turbine is a restriction.
the drive pressure couldnt be there without the heat of the combustion. . .the turbo is run off heat energy theres no way you can put it to disprove the physics behind this.
If you take any gas at a certain temperature, and lower it's pressure, it's temperature drops.
It's a cart-before-the-horse sort of thing. Which is it? That the turbo is directly using heat as a power source? Or that the turbo is a restriction in the exhaust flow, causing a pressure drop, causing lower temperatures after the turbo? the pressure variation wouldnt be there without energy to make it so (a pressure variation requires energy)! heat is the only source of energy!!!!!
Cargo Master
Joined: Jan 2005
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I don't have anything against cummins. I wouldn't go that route. How much is that gonna cost me? What am I gonna net from it? I'm happy w/ my psd. I'll just fix it. I have thought though that ford should have had different engine brand options since the psd was out sourced. That would have been cool.
FTE Leadership Emeritus
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From: Melbourne, Aus
Art, without trying to sound patronizing, look at it this way.
Engines are typically looked at it in terms of thermal energy. From a given amount of thermal energy that a gallon of fuel provides, how much kinetic energy is given out.
The standard combustion engine has the following process.
Fuel ignited -> heat -> fuel/air mix expands in pressure due to heat and presses cylinder down -> rotates crankshaft
The input is thermal energy, the output is kinetic energy. As part of this process, pressure is generated, but the thermal energy is the source (well, chemical energy is actually... but lets not get ahead of ourselves)
A turbo is merely part of that. A centrifugal fan (i.e. turbo) is great way of converting high volume, low pressure differentials into kinetic energy, just like a positive displacement pump (piston engine) is good and converting high pressure differentials into energy. You don't ever state that pressure is consumed by the engine, you state that heat is. Just like a turbo, it converts the heat to pressure, to kinetic.
The engine extracts all the energy it can in the process, and dispells the rest in the form of thermal energy through the coolant and exhaust system. The Turbo is merely a form of converting that thermal energy to pressure energy, and then converting that to kinetic energy, subsequently giving the engine a higher thermal efficiency.
I might add - this is a good discussion
Engines are typically looked at it in terms of thermal energy. From a given amount of thermal energy that a gallon of fuel provides, how much kinetic energy is given out.
The standard combustion engine has the following process.
Fuel ignited -> heat -> fuel/air mix expands in pressure due to heat and presses cylinder down -> rotates crankshaft
The input is thermal energy, the output is kinetic energy. As part of this process, pressure is generated, but the thermal energy is the source (well, chemical energy is actually... but lets not get ahead of ourselves)
A turbo is merely part of that. A centrifugal fan (i.e. turbo) is great way of converting high volume, low pressure differentials into kinetic energy, just like a positive displacement pump (piston engine) is good and converting high pressure differentials into energy. You don't ever state that pressure is consumed by the engine, you state that heat is. Just like a turbo, it converts the heat to pressure, to kinetic.
The engine extracts all the energy it can in the process, and dispells the rest in the form of thermal energy through the coolant and exhaust system. The Turbo is merely a form of converting that thermal energy to pressure energy, and then converting that to kinetic energy, subsequently giving the engine a higher thermal efficiency.
I might add - this is a good discussion
FTE Leadership Emeritus
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From: Long Island USA
When you compress a gas, it's temperature increases, and conversely when you reduce the pressure it's temperature decreases.
The engine is pumping exhaust out, the turbo is in the way increasing pressure before the turbo, and exhaust temp increases slightly because of compression. As it leaves the turbo, the pressure drops, lowering the temperature again.
Depending on the amount of the restriction, which is almost directly related to the transfer of mechanical energy from the exhaust flow to the turbo wheel and how hard the turbo has to push against the intake turbine wheel, the pressure will drop enough that the output temperature is a lot lower than you would expect.
It's not that the turbo is USING HEAT to produce power. It's that the power transfer causes a pressure drop that causes the lower temperature of the exhaust gas.
Now, we can get into how much temperature rise there is in the intake, versus the drop in the exhaust, and how much the intercooler plays into shedding that waste heat in the intake charge.
