Which is more fuel efficient - Jet or Piston?

[BoyntonStu]

Which is more fuel efficient - Jet engines or Piston engines?

IOW What is the main reason for choosing jet over piston?

BoyntonStu

[mytoyotasucks]

Which is more fuel efficient - Jet engines or Piston engines?

IOW What is the main reason for choosing jet over piston?

BoyntonStu

Now u talking Jet or turbine????

if u remember many years ago Chrysler had a car with a turbine in it and got about 100 MPG and they were scraped.

Now a jet just eats fuel compared to a piston engine.

But a jet can make way more power.

[BoyntonStu]

Now u talking Jet or turbine????

if u remember many years ago Chrysler had a car with a turbine in it and got about 100 MPG and they were scraped.

Now a jet just eats fuel compared to a piston engine.

But a jet can make way more power.

But a jet can make way more power. Correct.

However for equal power why choose jet over piston?

"Chrysler had a car with a turbine.."

From WIKI:

Its power turbine was connected, without a torque converter, through a gear reduction unit to an otherwise ordinary TorqueFlite automatic transmission. The flow of the combustion gases between the gas generator and free power turbine provided the same functionality as a torque converter but without using a conventional liquid medium. Twin rotating recuperators transferred exhaust heat to the inlet air, greatly improving fuel economy. Varying stator blades prevented excessive top end speeds, and provided engine braking on deceleration. Throttle lag, high fuel consumption — 17 miles per US gallon (14 L/100 km; 20 mpg-imp) — and exhaust gas temperatures at idle plagued early models. Chrysler was able to remedy or mitigate most of these drawbacks and deficiencies.


(However it never got even close to 100 MPG.)

BoyntonStu

[mytoyotasucks]

But a jet can make way more power. Correct.

However for equal power why choose jet over piston?

"Chrysler had a car with a turbine.."

From WIKI:

Its power turbine was connected, without a torque converter, through a gear reduction unit to an otherwise ordinary TorqueFlite automatic transmission. The flow of the combustion gases between the gas generator and free power turbine provided the same functionality as a torque converter but without using a conventional liquid medium. Twin rotating recuperators transferred exhaust heat to the inlet air, greatly improving fuel economy. Varying stator blades prevented excessive top end speeds, and provided engine braking on deceleration. Throttle lag, high fuel consumption — 17 miles per US gallon (14 L/100 km; 20 mpg-imp) — and exhaust gas temperatures at idle plagued early models. Chrysler was able to remedy or mitigate most of these drawbacks and deficiencies.


(However it never got even close to 100 MPG.)

BoyntonStu

OK im going to have to find the book i have on that Chrysler turbine.

[Painless]

Hmm... why choose a jet over a piston...

The first thing that springs to mind is that the energy of the jet is applied directly where as with a piston engine, the force is applied through the piston, crank and other components, this introduces mechanical loses.

[BoyntonStu]

Hmm... why choose a jet over a piston...

The first thing that springs to mind is that the energy of the jet is applied directly where as with a piston engine, the force is applied through the piston, crank and other components, this introduces mechanical loses.

Jets are more RELIABLE than pistons.

Pistons are more fuel efficient.

BoyntonStu

[Philldpapill]

Jet engines consume massive amounts of fuel, and have a ****-poor fuel to power conversion ratio. Piston-Cylinder engines typically get alot more mechanical power conversion since the exhaust is cooler(more heat gets turned into work). As far as the reliability factor goes... I never knew Jet engines were MORE reliable. I could be wrong about that, but typically, the more complicated and high-precision oriented a device gets(Jet engines), the LESS reliable they are.

@Painless, the mechanical losses really are minimal, accounting for less than 1% in modern cars. The vast majority of loss comes in due to the crappy thermal properties of the engine material itself. Ideally, we would have a material with extremely high thermal resistance, and very low specific heat properties. This way, little heat is transfered to the engine itself, which would be wasted work.

[Q-Hack!]

Jets are more RELIABLE than pistons.

BoyntonStu

Citation needed. Not sure I agree with this.

Now, if you had said that a scramjet engine is more reliable than pistons, I would have agreed. Since there are no moving parts in a scramjet. However the amount of maintenance required to keep a jet engine flying is much more than a standard piston engine. On most jets you usually break the entire engine down for a full inspection every 500 hours. The FAA requires a die sublimation test which causes cracks in the metal to show up. I suspect that if you did that same level of maintenance on a piston engine you would see the reliability rate increase; since you would catch any problems before they occur.

[Philldpapill]

Q-Hack!, well said.

BoytonStu, your OP is simple. Piston-Cylinder engines are more fuel efficient, while jet engines typically are capable of higher power per unit engine weight. They ARE fuel hogs though, with their Power/Fuel consumption ratio rather poor.

[gashead]

this is probably irrelevant, but ive seen many gasoline powered doorslammers ( pro mods ) out run the jet powered dragsters.
just a comment.