Date: Wed, 23 Nov 2011 08:47:48 -0600
Reply-To: ralph meyermann <ralphmeyermann@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: ralph meyermann <ralphmeyermann@GMAIL.COM>
Subject: Re: Vanagon? Really? Gasoline vs. Diesel
In-Reply-To: <CAAj276zHr3hRGErg2rkqpGh2dY1_z48YrFS+ZiZAGjXpzeTd1A@mail.gmail.com>
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The diesels in small vehicles is limited but vastly improving on the
performance and mileage over the past 15 yrs, on our old f350 gasser to the
f350 powerstroke we got a bunch more power/torque and doubled our pulling
fuel economy from 6mpg to 14 mpg! I would like to do a tdi upgrade from my
na wich will improve my emissions and torque/power a higher ratio tranny to
get more speed out of my turtle of a westy and keep same economy if not
better and possibly pull my small/light fishn boat too!!
Velma 82diesel 1.6 na westy
On Nov 23, 2011 12:01 AM, "Dennis Haynes" <d23haynes57@hotmail.com> wrote:
Over the years there are a number of folks that somehow get convinced that
Diesel is the way to go and consider ways to convert. There is always the
question of why more diesels are not available. This may be more of a Friday
topic but I'll try to shed some light. Of wonderful note we are starting to
see some interesting technologies for both gasoline and Diesel engines but I
see a number of forces that will keep Diesel use for small vehicles limited.
For one thing the new clean fuel requirements and other forces are making
Diesel fuel too expensive. Even home heating oil is going up. On this
current trip from New York to Florida I have witnessed as much as a $.80
price difference from regular unleaded to Diesel. That alone wipes out the
25% fuel economy improvement if that's what you get. Many Diesel vehicles
2007 and newer also require the use of a special Diesel Exhaust Fluid,
(DEF). This is a urea based fluid used to mix with the exhaust in the
catalytic converter to reduce the oxides of nitrogen (NOx) emissions. Due to
high compression ratios and the excess air, diesels make a lot of NOx. An
awful lot. This is a primary contributor to smog and why Diesel cars sales
were not allowed in many Northeast states from 2003 to 2006. I don't know
how much DEF is used per mile but I see the truckers by it in five gallon
pails.
Another big issue is both the increased purchasing and operating costs.
Gasoline engine technology is now to the point that there is very little
scheduled maintenance and almost any engine out there now can go 150,000 to
250,000 miles. Diesels have very expensive injection systems and all have
turbo chargers. The turbo alone can be a huge maintenance hit when it fails
and many will at around 100,000 miles or less. Often a turbo failure will be
the bearing assembly. This can allow engine oil to enter the intake track
and when the engine sucks it in the engine can go into a run away. No way to
shut it down until it blows. I have seen a number of Cat engines fail this
way. The new Diesel injection pumps and injectors have very tight tolerances
and any contamination will quickly destroy them. The final filters on many
of them filter to 2 micron.
So why do Diesels get better fuel economy? There are three main advantages
to a Diesel. Diesel fuel has a higher BTU content than Gasoline, operates
at higher compression, and the biggie is the lack of a throttle. Why does
the throttle thing help economy? To begin with you do not have the vacuum or
pumping losses. The inlet is always wide open so each intake stroke takes in
as much air as can be sucked in or that the turbo can force in. With a gas
engine when you lift your foot the engine and the vehicle slows down. With a
Diesel the vehicle will only slow down if going uphill or going fast enough
for wind resistance to slow you down. No energy is used to suck the air fuel
mixture through a throttle plate. Now since an engine produces power by
heating-expanding gases, having the cylinders fully charged with air, turbo
pressurized air any fuel burn is going to produce a much greater pressure
change, (power) than a partially charged cylinder would as in a gas engine.
This really gives the Diesel an advantage at partial load, low speed
operations. To add further to control emissions, modern Diesel injectors do
not simply shoot fuel into the cylinder at the right time. They actually
inject in steps to what is known as wave shaping. They start with a small
shot to get a burn going, then go for a power shot and then an after burn to
clean up soot. Yes for each cylinder power stroke the injector can fire
three times are some variable amount during the full power stroke. This
makes for complicated injectors as they not only operate electrically but
the electric part operates a pilot or control valve in each cylinder and
then depending on the injector design either high pressure fuel or engine
oil actually hydraulically operates the injector pin. This is often known as
a Hydraulic Electric Unit Injector, (HEUI). On some engines these are
calibrated so tight then when replacing them the replacements get stamped
with trim numbers to reflect differences from the ideal standard. When
installed you need to go into the ECU and program the trim numbers for the
new injectors and the cylinders they were installed in.
A Gasoline, (spark ignition) engine has to run with a controlled fuel-air
mixture. In order for the engine to run at a given RPM, it has to have a
certain volume of air and that volume has to have a matching, (14 to1)
amount of fuel go with. The Diesel does not need this. Note that in some
applications Diesels are also run with propane or natural gas.
So where are we going with this. We are starting to see gasoline engines
that will be direct injection and at some point we will see them going to
compression ignition. The wave shaping technology described above will allow
gasoline to be burned at much wider mixture ranges. So for idle and low
speed we can use the spark ignition and normal mixture control for
smoothness and when under way go to compression ignition, maximum air
intake, and maximum power and efficiency. This along with Hybrid technology
is going to be the future for automobiles and light trucks. Diesels will
still have their place for industrial and large truck, locomotives,
generators etc. but the new stuff will be complicated and until these new
technologies get refined somewhat expensive to maintain.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Mike S
Sent: Saturday, November 19, 2011 11:25 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Vanagon? Really?
At 10:45 PM 11/19/2011, Dennis Haynes wrote...
>As Gasoline engines go to
>direct injection and dual mode, (spark ignition to compression
>ignition) the
>Diesel advantages will disappear.
Compression ignition _is_ Diesel. It's not a matter of what fuel it uses.
