Depends on the application. By using a turbo motor, a car maker can use a smaller engine, which may save fuel when the turbo is not fully engaged, such as idling in stop and go traffic. This is purely speculation on my part, however.
turbo charged or naturally aspirated most fuel efficient??
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Guys, I'd say that it's a toss up in today's world with modern fuel injection and turbocharging technology. My old turbo car would get unbeatable mileage if I laid out of the boost really hard. Just cruising on the interstate though, the turbo does all the work on steep hills and such; once it spools just a hair, you can lay off the throttle a bit and get amazing gas mileage. Look at the mileage that Saabs get.
More efficient in the real world? It depends on a lot of factors.
Same displacement turbo vs NA (1.9L 200hp vs 1.9L 130hp).....NA will be more fuel efficient.
Similar power turbo vs NA (1.9L 200hp 4-cyl vs 3.0L 200hp 6 cyl)....turbo will be more fuel efficient.
Example:
My S40 has a low pressure turbo(7.5psig) 1.9L engine. On boost it breathes and makes as much power as a 6-cyl engine. Power band is wide with not much turbo lag so it feels like a smooth 6 under the hood. I get 24 city and 32-37 on the highway. The car would get lower fuel economy and handle poorly with the extra weight of a V6 under the hood.
Same displacement turbo vs NA (1.9L 200hp vs 1.9L 130hp).....NA will be more fuel efficient.
Similar power turbo vs NA (1.9L 200hp 4-cyl vs 3.0L 200hp 6 cyl)....turbo will be more fuel efficient.
Example:
My S40 has a low pressure turbo(7.5psig) 1.9L engine. On boost it breathes and makes as much power as a 6-cyl engine. Power band is wide with not much turbo lag so it feels like a smooth 6 under the hood. I get 24 city and 32-37 on the highway. The car would get lower fuel economy and handle poorly with the extra weight of a V6 under the hood.
Depends on application.
Turbo engines will operate off O2 feedback in closed loop and have same efficiency. At WOT, it will go to fuel MAPs depending on boost, RPM, temperature etc and run richer.
My 86 Daytona with 2.2 Turbo and +20 injectors gets as good mileage if not better than when it was stock and much better then the TB injected version of the same engine. It will get 32 MPG highway.
Turbo engines will operate off O2 feedback in closed loop and have same efficiency. At WOT, it will go to fuel MAPs depending on boost, RPM, temperature etc and run richer.
My 86 Daytona with 2.2 Turbo and +20 injectors gets as good mileage if not better than when it was stock and much better then the TB injected version of the same engine. It will get 32 MPG highway.
Here are three of the more significant advantages of diesel:
1. Diesel is more dense than gas, so you get more energy per given volume. And we buy fuel based on volume and not mass.
One gallon of diesel contains approximately 147,000 BTUs of energy, while a gallon of gasoline only has 125,000 BTUs.
2. Direct-injection of fuel in to the combustion chamber means less unburned fuel compared to a port-injection setup that sprays fuel before the combustion chamber.
This advantage goes away when direct injection gas engines are taken into account, though these are somewhat rare.
3. Reduced pumping losses, since diesels are unthrottled.
1. Diesel is more dense than gas, so you get more energy per given volume. And we buy fuel based on volume and not mass.
One gallon of diesel contains approximately 147,000 BTUs of energy, while a gallon of gasoline only has 125,000 BTUs.
2. Direct-injection of fuel in to the combustion chamber means less unburned fuel compared to a port-injection setup that sprays fuel before the combustion chamber.
This advantage goes away when direct injection gas engines are taken into account, though these are somewhat rare.
3. Reduced pumping losses, since diesels are unthrottled.
diesel turbo > gas turbo in terms of straight efficiency.
However, if you want 500hp out of a 4cyl, versus 500 out of an N/A application, your turbo will be fairly efficient "off boost" whereas the N/A car will guzzle all the time.
If you're comparing 2.0 vs. 2.0 then it's silly. Honda civics use something like 250cc/min injectors, whereas stock DSM's use 450cc- which is why when honda guys go to turbo they upgrade those first. I'm going to be running 750cc injectors on the Galant, and probably 1000cc injectors on the talon.
Efficient for the amount of power, i guess.
However, if you want 500hp out of a 4cyl, versus 500 out of an N/A application, your turbo will be fairly efficient "off boost" whereas the N/A car will guzzle all the time.
If you're comparing 2.0 vs. 2.0 then it's silly. Honda civics use something like 250cc/min injectors, whereas stock DSM's use 450cc- which is why when honda guys go to turbo they upgrade those first. I'm going to be running 750cc injectors on the Galant, and probably 1000cc injectors on the talon.
Efficient for the amount of power, i guess.
I disagree with you on that point. The forced induction S.I. engines almost invariably show a poorer Brake Specific Fuel Consumption than their naturally aspirated counterparts, which, by definition is thermal efficiency.
And in the real world, which is predominantly throttled driving, the lower compression ratio gives you a lower expansion ration, and poorer efficiency under that regime also.
Pull out some BSFC maps for speed and load, and see for youself (Internal Combustion Engine Fundamentals by J.B. Heywood has such maps).
Similarly, turbo diesels generally show lower BSFCs through their operating range.
I purposely left turbo-compounding, as it's applicable to naturally aspirated engines as well as forced induction.
Forced induction in aircraft engines is predominantly to get them breathing sea level (or higher) pressure air at altitude.
This gets back to the argument that a small turbo engine CAN use less fuel than a large naturally aspirated engine (at a lower thermal efficiency for the engine).
If an aircraft needed 1000hp at cruise speed, it could be obtained by a 10 litre engine at sea level. At altitude, it might need a 25 or 30 litre engine (physically more massive), or have forced induction, allowing the 10 litre to breath sea level air at oeprating height.
Generally, the 16:1 are direct, rather than prechamber diesels, which further reduce pumping losses and heat loss to coolant, gaining efficiency.
I really like my turbo diesel truck, as much as some of the motorcyles that I use to have. It's not a very good 1/4 mile or top engine machine, but it is fun on the hills. Hearing a bit of whine once in awhile is nice, and it works very well. On our last vacation trip we hit 20 mpg on the stretch thru the passes on I5 from the Bay Area in CA to central Oregon, in a 3/4 ton 4x4 quad cab pickup with a canopy. I'm guessing I could do low 20s in flatlands.
Sorry, but I have to disagree on both counts.
Turbos, especially intercooled ones, increase efficiency by extracting wasted heat energy from the exhaust gasses. If correctly designed, the drop in compression ratio in spark ignition engines is small and there is still a net gain in overall efficiency. Without turbocharging or turbocompound, a related technology, piston-engined airliners would never have been able to fly thousands of miles without refuelling stops.
Turbocharged deisels typically have a 16:1 compression ratio vs above 20:1 for many NA diesels.
I haven't seen a big advantage of the two-cycles mentioned. Fewer parts and less weight. It means a lot on a lightweight motorcycle or that string trimmer you have to carry around.
Love that Stihl string trimmer I have.
And, remember the old RD350? Great power, low weight. You had to have a huge 4 cycle to beat it.
The commercial Toro 21" mowers with the 2 cycle Suzuki is not being made any longer (EPA), but they are highly coveted.
Jack
Love that Stihl string trimmer I have.
And, remember the old RD350? Great power, low weight. You had to have a huge 4 cycle to beat it.
The commercial Toro 21" mowers with the 2 cycle Suzuki is not being made any longer (EPA), but they are highly coveted.
Jack
One needs to be careful about comparing fuel usage in engines of the same size vs the same power output, but I think that Shannow acknowledged that.
On 2 strokes, I had an RD400, which was one of my favorites. At one time Harley and Triumph were racing 750s while Yamaha was running the 350.
http://www.honeywell.com/sites/ts/tt/turbo_feature.htm
Honeywell Celebrates 100 Years of Turbo; 50th Year of Garrett® Turbocharged Vehicle
The turbo — more relevant than ever to modern needs
Turbochargers harness and recycle the energy produced by automobile engines, by using exhaust gas energy (speed and heat) that would otherwise be lost and transforming it into power. As a result, turbocharged engines deliver significant fuel cost advantages over their naturally-aspirated counterparts. Because a turbocharger delivers more air to the engine, fuel combustion is easier, more thorough and therefore cleaner.
For gasoline passenger cars, where the trend is for smaller displacement engines, turbos contribute to CO2 reduction by delivering 10-20% better fuel efficiency than a non-boosted car of equal power. In turbo diesel vehicles, the fuel efficiency gain is 30-50% better than a non-boosted gasoline vehicle. These gains help meet the increasingly demanding emissions standards being applied in the US, Europe, and Asia.
On 2 strokes, I had an RD400, which was one of my favorites. At one time Harley and Triumph were racing 750s while Yamaha was running the 350.
http://www.honeywell.com/sites/ts/tt/turbo_feature.htm
Honeywell Celebrates 100 Years of Turbo; 50th Year of Garrett® Turbocharged Vehicle
The turbo — more relevant than ever to modern needs
Turbochargers harness and recycle the energy produced by automobile engines, by using exhaust gas energy (speed and heat) that would otherwise be lost and transforming it into power. As a result, turbocharged engines deliver significant fuel cost advantages over their naturally-aspirated counterparts. Because a turbocharger delivers more air to the engine, fuel combustion is easier, more thorough and therefore cleaner.
For gasoline passenger cars, where the trend is for smaller displacement engines, turbos contribute to CO2 reduction by delivering 10-20% better fuel efficiency than a non-boosted car of equal power. In turbo diesel vehicles, the fuel efficiency gain is 30-50% better than a non-boosted gasoline vehicle. These gains help meet the increasingly demanding emissions standards being applied in the US, Europe, and Asia.
% throttled operation adds to the confusion. A SI engine operates at lowest BSFC under unthrottled, or near unthrottled conditions.
A smaller turbocharged SI engine that is designed for economy will be operating closer to unthrottled condition than a larger naturally aspirated engine. That gains back part, maybe more than all of the advantage the naturally aspirated engine has because of it's higher compression ratio.
Remember that an intercooled turbo and its related components, add about 100 pounds to an engine. With modern alloy blocks, heads and such, there really isn't that much weight difference between 4 cyl's and V-8's. Throw a turbo on the 4 and the weight difference is negligable. A turbo 4 should allow tighter packaging though and therefore would fit into a smaller car.quote:
Originally posted by Gary Allan:
The basic difference that I see is ..little engine..lots of power. It allows more design flexiblity with a lighter, and perhaps smaller, power plant. If you need 190 hp to propell a vehicle in an acceptable manner. You can use 4.2 liters ..or 2.5 liters. One may weight 350-400 lbs. the other 240 lb (or less). One will have perhaps 6 cylinders ..the other 4.
There is replacement for displacement ..it's just not cheap.
Turbochargers also increase backpressure which decreases fuel economy as compared to a NA engine. Big turbos don't really do much until the RPM's get above about 3k.
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