Does engine revs alone determine fuel used, regardless of accelerator use?

[delmarrey]

When I drive my 7.3L diesel truck unloaded between Seattle and SF I get 16 mpg. The same trip with a 18000 lb 5th wheel it gets 11.5 mpg.

Hp and speed take fuel, and the heavier and faster will take even more fuel no matter what, and that's all there is tuit.
Energy takes fuel. Some fuels are more efficient. E.g. Natural gas vs electrical heating, gravity/hydro vs solar production, diesel vs gasoline. It all comes down to budget and longevity.

[a64pilot]

If you really are curious about decreasing fuel consumption, google "pulse and glide" and Hypermileing
I used to more as a curiosity than anything else, I think I got an over 70 MPG average out of the Prius Hypermileing it once for a considerable distance

[FlyingCloud1937]

You cant compare a gas to a diesel engine. That being said we mostly have diesel engines.

In my boat a 52 foot, with twin Perkins 6-354's. I'll give you an example of why RPM isn't the deciding factor on fuel consumption.

When I run my engines at the dock at 1300 RPM in neutral my pyrometers read 275 F, now my boat has a plumb bow, and I don't like to run my engines with no load, so I slowly push the stem into the dock, and run it at 1300 RPM, the pyros now read 450 F. Now when I am on the water and running 1300 RPM, my pyros read 300 F, and I am doing 6.5 knots.

When I am cruising I cruise at 2200 RPM I am doing 10.5 knots over ground by GPS, in no wind and no current, the pyros read 600 F. Now add a 10 knot head wind and the pyros read 625 F, and my speed is down to 10 knots.

Now cruising at the same 2200 RPM, with no wind and running into a 4 knot current, my pyros read 675 F, and my speed over ground is down to about 9 knots.

Lloyd

[valhalla360]

Originally Posted by FlyingCloud1937

You cant compare a gas to a diesel engine. That being said we mostly have diesel engines.

In my boat a 52 foot, with twin Perkins 6-354's. I'll give you an example of why RPM isn't the deciding factor on fuel consumption.

When I run my engines at the dock at 1300 RPM in neutral my pyrometers read 275 F, now my boat has a plumb bow, and I don't like to run my engines with no load, so I slowly push the stem into the dock, and run it at 1300 RPM, the pyros now read 450 F. Now when I am on the water and running 1300 RPM, my pyros read 300 F, and I am doing 6.5 knots.

When I am cruising I cruise at 2200 RPM I am doing 10.5 knots over ground by GPS, in no wind and no current, the pyros read 600 F. Now add a 10 knot head wind and the pyros read 625 F, and my speed is down to 10 knots.

Now cruising at the same 2200 RPM, with no wind and running into a 4 knot current, my pyros read 675 F, and my speed over ground is down to about 9 knots.

Lloyd

In general, gas and deisel are similar but there are some particulars to account for.

I understand what you mean by reading the temps but for the common man, if you motor into a 20kt wind with the RPM at 2000 and then do a 180 and have the wind at your back, you will have to reduce the throttle setting (ie: use less fuel) to keep the RPM at 2000 and you will likely be traveling faster further improving your fuel consumption.

RPM by itself doesn't tell you fuel consumption unless everything else is held constant.

[a64pilot]

Originally Posted by FlyingCloud1937

Now cruising at the same 2200 RPM, with no wind and running into a 4 knot current, my pyros read 675 F, and my speed over ground is down to about 9 knots.

Lloyd

That is interesting, boat only "sees" speed through the water and air resistance, if anything you should have a very slightly higher speed through the water and a very slightly lower EGT, reason is the only difference current makes assuming zero wind speed is a slightly lower wind speed over the deck.
You only lose 1.5 kts ground speed going into a 4 kt current?

[FlyingCloud1937]

I measure, my speed over ground by Simrad GPS, I measure speed through the water by Fruno LS 6100. The Fruno is calibrated at 200 RPM 10.5 Knot cruise on Lake Washington no current, and no Wind to match the speed over ground by the Simrad.

The hull design is a semi-displacement by Ed Monk Sr. 1937. He is known for his efficient hull designs as much as he was for his Cabin exterior and interior design.

This is her at flank speed of 14.5 not over ground at 2400 RPM lake Washington.



Lloyd

Originally Posted by a64pilot

That is interesting, boat only "sees" speed through the water and air resistance, if anything you should have a very slightly higher speed through the water and a very slightly lower EGT, reason is the only difference current makes assuming zero wind speed is a slightly lower wind speed over the deck.
You only lose 1.5 kts ground speed going into a 4 kt current?

[FlyingCloud1937]

Typo
The Fruno is calibrated at 2200 RPM 10.5 Knot cruise
This is her at flank speed of 14.5 not over ground at 2500 RPM Lake Washington.

Lloyd

Originally Posted by FlyingCloud1937

I measure, my speed over ground by Simrad GPS, I measure speed through the water by Fruno LS 6100. The Fruno is calibrated at 200 RPM 10.5 Knot cruise on Lake Washington no current, and no Wind to match the speed over ground by the Simrad.

The hull design is a semi-displacement by Ed Monk Sr. 1937. He is known for his efficient hull designs as much as he was for his Cabin exterior and interior design.

This is her at flank speed of 14.5 not over ground at 2400 RPM lake Washington.



Lloyd

[FlyingCloud1937]

This is her at flank speed of 14.5 knots over ground at 2500 RPM Lake Washington.

Originally Posted by FlyingCloud1937

Typo
The Fruno is calibrated at 2200 RPM 10.5 Knot cruise
This is her at flank speed of 14.5 not over ground at 2500 RPM Lake Washington.

Lloyd

[zeehag]

hell ye lost me at accelerator.
i cannot find one on my boat.
mebbe ye has cars and boats cornfuzzled somewhat.
they is a bunch different.
moreso than merely apples and oranges.

[onestepcsy37]

Translating his word to ZeeSpeak, an accelerator is also known as a throttle.