What are These Cars Worth?

[asavage]

Well maybe this needs updating soon, if not now, with the sudden surge in fuel prices in the last couple of weeks. That should make diesels more valuable again.

Diesels in general, yes, but the Maxima diesel doesn't get much better mileage than a lot of newer, more modern cars. Buying a Maxima diesel for the mileage is a hard sell. I get merely high 20s, not spectacular mileage by today's standards for a small to mid-size wagon. I could probably do as well with an early-90s Camry wagon, even with the V6.

[fud2468]

I would certainly agree with you as far as highway mileage is concerned, however my goal was better economy around town. From what's been said on thes site, we don't dare go very far in these anyway, or very fast.
At part throttle, can't 30 to 50 % better mileage be expected as compared to a gasser of the same size/weight?
But if not, there's the possibility of alternative fuels.
Hmmmm--I wonder if a diesel will run on producer gas from wood chips?
Ray Mac

[asavage]

But if not, there's the possibility of alternative fuels.

Which is the biggest reason I'm with the LD28. Biodiesel: domestically produced, carbon neutral, cleaner burning, compatible with existing infrastructure/distribution. When we have a surplus of electricity to produce hydrogen for this bullshit "hydrogen economy", I'm right there with electric cars and/or fuel cells. Until then, biodiesel for me.

Hmmmm--I wonder if a diesel will run on producer gas from wood chips?

No. A diesel engine has to have its fuel injected, not aspirated.

[fud2468]

Yes, the injectors would still have to squirt fuel in to start the fire, but would the engine then run on the gas mixture?
Producer gas has hydrogen & carbon monoxide as the combustible gases IIRC, but with a lot of noncombustble gases & ash as well, which is a problem, of course.

[asavage]

Yes, the injectors would still have to squirt fuel in to start the fire, but would the engine then run on the gas mixture?

No. If you put enough fuel in to contribute > (guessing, ballpark) 10% output, it will self-ignite. If you use less, the mixture is too lean to self-ignite, but you get so little benefit (add'l output) that it's not worth the equipment and installation relative to the benefit. Remember, you have to use energy to compress the waste gas to carry it with you, and that's a big problem with gases such as natural gas (CNG) that cannot be liquified at low pressures, and have to be compressed to over 2000 or 3000 PSI to get reasonable energy density for transport.

That's also why LPG (Liquified Propane Gas, which isn't actually 100% propane or anything near it) is a good alternative fuel: it can be liquified at low pressure so it doesn't require a huge amount of energy input to compact it to a reasonable energy density to distribute and carry onboard.

I'm a fan of LPG, and I have conversion equipment here to do a conversion someday (IMPCO 425 mixers, 300a mixer, Model E vapouriser/regulator, VFF30 lockoff/filter), except the tank and controller, but most LPG in the US is made from natural gas, so though it burns very cleanly -- and is exceptionally easy on lubricating oil -- it's still not carbon neutral and isn't made entirely domestically. It's also about 10% less energy-dense per unit volume (gallon) than gasoline, so your MPG drops with LPG use on a "light" gasoline engine conversion. Gaseous fuels also displace air in the intake, unlike gasoline that is still much a liquid until it actually gets into the combustion chamber. Because propane etc displace intake air, you can't get as much air/fuel mix into the engine, which slightly lowers the oveall volumetric efficiency on a conversion. A "proper" propane conversion ups the compression ratio to take advantage of propane's higher octane rating, thereby increasing the engine's thermal efficiency and offsetting the air displacement and lower energy density pitfalls. But then you can't "dual fuel" anymore. Propane burns hotter than gasoline by approx. 150°F and for that reason exhaust valves should be of the best material, and older engines esp. should have their valve seats replaced to harder material, if the existing seats are std. cast iron.

That's just the high points of LPG vs gasoline; not really relevant to diesel.

What you suggest (gas fumigation of diesel engine) is what the propane "injection" guys are doing (by and large the "barbeque tank" crowd), and if you over-fuel with a gaseous fuel (aspirated) in a diesel, all you get is early ignition, very high EGTs, and holed pistons.

Producer gas has hydrogen & carbon monoxide as the combustible gases IIRC . . .

Carbon monoxide is not flammable. It can be oxidized (with a largish negative energy balance) to carbon dioxide, but you don't get enough energy out of this reaction to do anything useful.

. . . but with a lot of noncombustble gases & ash as well, which is a problem, of course.

Noncombustibles is what EGR is all about, so it's not necessarily a bad thing to not be able to be readily oxidized

Now ask me about methane

I'm hoping for Themal Depolymerisation to save the day. But I'm putting my money on algae-as-feedstock-based biodiesel.

[fud2468]

Very enlightening, Al (no pun intended). I am re-reading it in order to have it sink in.
I guess that for one thing, I have to educate myself a great deal more on terminology and theory of these things.
All I know about methane is that it won't liquify under pressure like propane unless pressure is extremely high. Am eagerly awaiting your opinion on it.
Thanks,
Ray Mac

[asavage]

When I was a kid, I was really gung-ho about methane and methane digesters (anaerobic bacteria in a vat: greens + manure + a bit of cellulose + a little heat - oxygen = methane). However, natural gas & methane share a common problem, as you & I already pointed out: you spend around 1/3 to 1/2 of the energy value of the fuel to liquefy it. For that reason, methane is best used in stationary applications such as space heating (greenhouses, etc.). It's quite a bit more efficient that way.