Date: Mon, 24 Jul 2000 11:50:04 -0400
Reply-To: Martin Jagersand <vwjag@hammer.cs.jhu.edu>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Martin Jagersand <vwjag@hammer.cs.jhu.edu>
Subject: Re: Engine Conversion and MPG
In-Reply-To: <01e501bff537$b083d760$b632510c@pavilion> (message from Karl Wolz
on Sun, 23 Jul 2000 23:23:24 -0700)
Karl Wolz Wrote:
> My understanding is that fuel economy is determined primarily by
> vehicle weight. frontal area and driving style. Changing the power
> plant should not have a significant effect on fuel economy, and
> your figures kinda bear this out.
Fuel economy depends on the vehicle, engine and driver. The two
first can easily be calculated. The behaviour of the driver is
hard to quantify, and therefore more difficult to take into
account.
1/ Vehicle drag can be measured, or calculated using friction coefficients
(for wind drag, tires...) For our Westy's I measured the drag at various
speeds and made the following graph:
http://www.cs.jhu.edu/~jager/vw/Yale/engine/diesel1.9/WestyDrag_12_98.gif
The method and experients required were posted and discussed on the
list at that time (fall 1998). See the archives.
2/ Engine efficiency is given in grams of fuel required to produce
one kWh (kilo Watt hour). These figures are also either measured on
a real engine, or calculated from engine and fuel injection pump data.
The specific efficiency of the VW IDI Diesel engines are about
200g/kWh and the TDI's 250g/kWh. The efficiency is really a function
of rpm and MEP (mean effective pressure in the cylinder, ie load),
but is reasonably constand between 1000-4000 rpm in the Diesels.
Gas engine efficiency varies a lot more. In general the engine and
transmission should be matched to the vehicle so it works at peak
efficiency at normal cruising speeds. This is true in most European
vehicles, where (choose one) a: people care about the environment,
b: fuel is expensive and people care about there wallet.
3/ For l/100km figures or MPG use 1/, 2/ and law of physics to integrate
over a specified driving cycle. A particularly simple example
is constant speed driving. Calculations for a westy with the IDI
diesel comes out to 26mpg at 60mph. Details and more examples
are at:
http://www.cs.jhu.edu/~jager/vw/Yale/engine/tdiswap/tdiswap.html
Cheers,
Martin
--
Westy 1.9l Turbo Diesel (Not for sale!!!)
Quantum 1.6l Turbo Diesel FOR SALE, See:
http://www.cs.jhu.edu/~jager/vw/Quantum/QuantumTD85.html
New and used parts for sale, gas and Diesel:
http://www.cs.jhu.edu/~jager/vw/Yale/forsale.html
Martin Jagersand email: vwjag@hammer.cs.jhu.edu
Computer Science Department
Johns Hopkins University
Slow down and visit the VW diesel Westy page:
WWW: http://www.cs.rochester.edu/u/jag/vw
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