Good idea or a complete lack of mechanical knowlege
Discussion
wca said:
Manufacturers seem to be moving to turbos to get the fuel economy figures without losing the power. I am not a big fan of forced induction based on experience (despite loving my supercharged V8 SLK).
I will start with a slightly clichéd description of the options at the moment.
Turbo chargers = good power, good economy, driving experience compromised through lag
Super charging = good power, constant mechanical drag effecting economy, good driving experience
Natural Aspiration = okay power, poorer economy, best engine response
Now imagine having an 'always on' turbo charged engine. Still the good economy and power but with normally aspirated like engine response.
I know Lancia and VW have done supercharged and turbocharged engine but this is a very mechanically complex system with lots of extra gubbins to fit into the engine bay.
What about this then - fit an electric motor into the turbo charger. The electric motor keeps the turbo spinning while it is 'off boost' and can be switched off once the turbo is up to speed. Less weight and complexity that a supercharger and wouldn't need massive batteries (weight) as it would only need to work at low revs. It could even recharge on overrun.
Any engineers want to shoot this idea down before I run off to the patent office?
Others will have commented already. But I think you've also confused turbo lag with boost threshold.I will start with a slightly clichéd description of the options at the moment.
Turbo chargers = good power, good economy, driving experience compromised through lag
Super charging = good power, constant mechanical drag effecting economy, good driving experience
Natural Aspiration = okay power, poorer economy, best engine response
Now imagine having an 'always on' turbo charged engine. Still the good economy and power but with normally aspirated like engine response.
I know Lancia and VW have done supercharged and turbocharged engine but this is a very mechanically complex system with lots of extra gubbins to fit into the engine bay.
What about this then - fit an electric motor into the turbo charger. The electric motor keeps the turbo spinning while it is 'off boost' and can be switched off once the turbo is up to speed. Less weight and complexity that a supercharger and wouldn't need massive batteries (weight) as it would only need to work at low revs. It could even recharge on overrun.
Any engineers want to shoot this idea down before I run off to the patent office?
Boost threshold is at what rpm you can make significant boost, i.e. 3500rpm. This is often confused as lag, but it isn't.
Turbo lag can happen at any rpm the turbo can make boost at, even the red line. Lag happens when you lift off the throttle, the sudden reduction in exhaust gas flow means the turbo cannot sustain significant boost. When you reapply the throttle (even if you lift off at 6000rpm for a second or two and did nothing else), there is a lag for the exhaust gas flow to increase, and a lag before the turbo will start making significant boost again (due to the turbines needing to spin up again and then to compress the air in the intake track and pipe work).
I've just had an idea - although probably not original - what about something like a decent capacity model aircraft petrol engine? Single cylinder, twin, radial even - bound to make enough HP/create enough pressure?
I get now that electric motors have their drawbacks but a decent output petrol engine? Could even have it's own LPG conversion.
I get now that electric motors have their drawbacks but a decent output petrol engine? Could even have it's own LPG conversion.
Many years ago, when I had just started at Sheffield uni (2002), I remember seeing an old turbodiesel truck engine in their test cell which had an experimental motor-generator sandwiched between the turbine and compressor housings. Externally all that was visible was the finned aluminium housing of the M-G, which was a bit smaller in diameter than the other housings, and some fairly beefy cabling running to it.
Chin wagging with one of the postgrads revealed that the device generated power when "on boost", enabling the removal of the alternator from the engine and thus reducing the fuel consumption, and also operated as a motor when initially coming onto boost to reduce the spool-up time.
That was 11 years ago (farking hell, now I feel old!), no idea what became of it, seemed a very clever idea to me and i'm a little surprised not to have seen something similar in production.
Chin wagging with one of the postgrads revealed that the device generated power when "on boost", enabling the removal of the alternator from the engine and thus reducing the fuel consumption, and also operated as a motor when initially coming onto boost to reduce the spool-up time.
That was 11 years ago (farking hell, now I feel old!), no idea what became of it, seemed a very clever idea to me and i'm a little surprised not to have seen something similar in production.
205alive said:
I've just had an idea - although probably not original - what about something like a decent capacity model aircraft petrol engine? Single cylinder, twin, radial even - bound to make enough HP/create enough pressure?
I get now that electric motors have their drawbacks but a decent output petrol engine? Could even have it's own LPG conversion.
Going on this...I get now that electric motors have their drawbacks but a decent output petrol engine? Could even have it's own LPG conversion.
Max_Torque said:
And a turbo charger will be shifting approx 50kW at peak power!
...I'd assume not.A model turboshaft engine, like the one on the hillclimb car in the video linked earlier, that seems to work.
Jonny_ said:
Chin wagging with one of the postgrads revealed that the device generated power when "on boost", enabling the removal of the alternator from the engine and thus reducing the fuel consumption.
Not sure about the logic of your 'thus'. I'd guess that in reality the engine was burning more fuel to drive the turbo and additional electrical load...Peak power output for peak power output, the turbocharged engine has better fuel economy when cruising along the motorway because it will be of smaller displacement and have less friction, also the turbo will barely be boosting. So instead of having a 3.0L NA engine you might use a 2.0L turbo , and on the motorway it will act as a 2.0L NA but be capable of providing the power of the 3.0L.
When turbos are on high boost, exhaust gas temperatures tend to rise pretty high and fuel tends to be added to control the temperatures to protect the catalysts. At medium boost the temperatures are less of an issue but you still need to drive the turbo compressor so you are subject to an issue of this consuming power, from the turbine stage and the compressor stage.
A good supercharger nowadays is actually a compressor, and at many engine operating points are more efficient than the turbochargers they replace. They also provide instantaneous throttle response.
Electric superchargers are of most use to 2 stroke diesels so they can start without additional compressors needing to be added.
When turbos are on high boost, exhaust gas temperatures tend to rise pretty high and fuel tends to be added to control the temperatures to protect the catalysts. At medium boost the temperatures are less of an issue but you still need to drive the turbo compressor so you are subject to an issue of this consuming power, from the turbine stage and the compressor stage.
A good supercharger nowadays is actually a compressor, and at many engine operating points are more efficient than the turbochargers they replace. They also provide instantaneous throttle response.
Electric superchargers are of most use to 2 stroke diesels so they can start without additional compressors needing to be added.
Mave said:
Not sure about the logic of your 'thus'. I'd guess that in reality the engine was burning more fuel to drive the turbo and additional electrical load...
The turbo gets most of it's energy (remember reading a figure of 80%, but can't recall where!) from the heat of the exhaust gases, which is otherwise wasted. So while I reckon you'd be correct in saying that this setup would require the engine to generate additional power (the extra loading on the turbo will increase exhaust back-pressure slightly, which in turn increases pressure on the piston during its exhaust stroke), overall the fuel consumption should decrease as the alternator loading previously driven directly from the engine is now driven mostly by waste exhaust heat.
If you're going to use electrickery to mask the torque deficit below the boost threshold, then you'd be better off hybrid-izing the powertrain and adding in the extra torque with an electric motor. Then you'd get some extra fuel-saving flexibility by utilizing the benefits of a hybrid drivetrain at (probably) similar money.
You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
Jonny_ said:
overall the fuel consumption should decrease as the alternator loading previously driven directly from the engine is now driven mostly by waste exhaust heat.
It's not waste heat though- it's heat that would otherwise be driving the piston. You've got a fixed expansion from cylinder peak pressure down to atmospheric, which gives you a pretty fixed amount of available power. All you are doing is extracting through a turbine instead of a piston...AER said:
If you're going to use electrickery to mask the torque deficit below the boost threshold, then you'd be better off hybrid-izing the powertrain and adding in the extra torque with an electric motor. Then you'd get some extra fuel-saving flexibility by utilizing the benefits of a hybrid drivetrain at (probably) similar money.
You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
How many batteries would I need and how heavy are they?You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
Mave said:
Jonny_ said:
overall the fuel consumption should decrease as the alternator loading previously driven directly from the engine is now driven mostly by waste exhaust heat.
It's not waste heat though- it's heat that would otherwise be driving the piston. You've got a fixed expansion from cylinder peak pressure down to atmospheric, which gives you a pretty fixed amount of available power. All you are doing is extracting through a turbine instead of a piston...Does the cylinder pressure even drop to atmospheric in a diesel cycle?
over complicated.
Al you need is a decent roller bearing turbo. A friend had a GT45 framed one a few years ago, it was making 5 psi by 1800rpm and could run in excess of 2 bar. Tried to find a spec sheet but can't. I can remember it just being really smooth, wasn't that expensive either IIRC
Al you need is a decent roller bearing turbo. A friend had a GT45 framed one a few years ago, it was making 5 psi by 1800rpm and could run in excess of 2 bar. Tried to find a spec sheet but can't. I can remember it just being really smooth, wasn't that expensive either IIRC
xRIEx said:
I don't understand how heat in the exhaust gases, i.e. already past the combustion chamber, could do work against a piston.
Does the cylinder pressure even drop to atmospheric in a diesel cycle?
I'm puzzled too. Mave, any way you can elaborate? I'm not an expert in this field, but always thought the turbocharger was a means of utilising the otherwise wasted heat of the exhaust gas (which leaves the cylinder at around 800 deg.C, and does no further work other than a small amount of pulse scavenging - velocity of gas in exhaust helps extract the gas from the cylinder during the next exhaust stroke - and dissipates the heat to the atmosphere).Does the cylinder pressure even drop to atmospheric in a diesel cycle?
Jonny_ said:
xRIEx said:
I don't understand how heat in the exhaust gases, i.e. already past the combustion chamber, could do work against a piston.
Does the cylinder pressure even drop to atmospheric in a diesel cycle?
I'm puzzled too. Mave, any way you can elaborate? I'm not an expert in this field, but always thought the turbocharger was a means of utilising the otherwise wasted heat of the exhaust gas (which leaves the cylinder at around 800 deg.C, and does no further work other than a small amount of pulse scavenging - velocity of gas in exhaust helps extract the gas from the cylinder during the next exhaust stroke - and dissipates the heat to the atmosphere).Does the cylinder pressure even drop to atmospheric in a diesel cycle?
It is true that the piston is working against the pre-turbine pressure, but in the scheme of things this isn't all that much work. What is useful work (and quite a bit of it) is expanding the exhaust gas again through another nozzle (which is what a turbine effectively is). You could let the gas expand through a fixed nozzle and get absolutely no work out of it whatsoever, but this is wasting resources.
Turbine energy isn't free, but it's pretty cheap!
Turbine energy isn't free, but it's pretty cheap!
odyssey2200 said:
AER said:
If you're going to use electrickery to mask the torque deficit below the boost threshold, then you'd be better off hybrid-izing the powertrain and adding in the extra torque with an electric motor. Then you'd get some extra fuel-saving flexibility by utilizing the benefits of a hybrid drivetrain at (probably) similar money.
You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
How many batteries would I need and how heavy are they?You're going to have a huge battery, high power electronics and lumps of iron and copper to cart around anyway...
AER said:
It is true that the piston is working against the pre-turbine pressure, but in the scheme of things this isn't all that much work. What is useful work (and quite a bit of it) is expanding the exhaust gas again through another nozzle (which is what a turbine effectively is). You could let the gas expand through a fixed nozzle and get absolutely no work out of it whatsoever, but this is wasting resources.
Turbine energy isn't free, but it's pretty cheap!
But if the piston is working against the pre-turbine pressure, then isn't that taking away expansion you could otherwise use in the piston? Isn't the work available from expanding from the pre-turbine pressure down to ambient the same, irrespective of whether you do it using a turbine or a piston?Turbine energy isn't free, but it's pretty cheap!
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