Adolph, these really aren’t constructive comments.
However, after your analogy has been decoded: As far as I can see, you’re making the point that it’s more efficient to use one truck (diesel or gasoline) than to use 65 cars (again, diesel or gasoline) if you want to haul 65 tonnes. How this can be used as an argument for diesel being more efficient than contra gasoline, I don’t know.
I believe it was Anthracite’s intention to point this out as well.
So, will you enlighten us to how your analogy points to diesel being more efficient than gasoline ?
OK, Adolph, this is how it should be compared, and I’ll try to keep it simple.
We’re buying two Volkswagen Golfs. You’re driving a 2.0 gasoline version, and I’m driving the 1.9 TDI (diesel) version. We’re both going to drive the same 100 km stretch. All the while, our exhausts are being measured by, I dunno, exhaust-measuring-equipment or something. After the 100 km, we read the measurements in terms of C02 out put. Also, we compare fuel mileage.
We will find, that although the diesel used less fuel (in liters/gallons - and in Europe also in MONEY), it produced MORE C02. Therefore, it is less efficient from an environmental point of view. Which is, incidently, the reason that most European countries require a higher road tax for a diesel car than for the comparable gasoline model.
The M1 Abrahms (and the variants) are able to operate on kersone, disel, gas, alchol and jet fuel. Note if you ever use Jet Fuel DO NOT ever use the smoke generator. It will belch out flame like a flame thrower.
A little more CO2 (maybe), but much more NOx and much more black smoke. However, if we were still talking about energy conversion efficiency, I would expect the diesel engine to perform up to 30% better than the petrol. Which could actually mean less CO2 from the diesel than the petrol.
Why are you doing this? I tried to point out that the analogy that your “mate” is using was not a valid one. I didn’t mock you or belittle you, rather I took the time to try and explain and give a counter-example to his analogy. I see Spiny Norman agrees with me; anyone else here think I misinterpreted Adolph’s analogy?
Maybe I really don’t have so much time on my hands after all, and maybe I shouldn’t keep trying to help people on various subjects where I might be able to (including making 4-page posts on coal that no one actually reads).
I’ll paraphrase the OP here, partly to see if I understood it right and since most of the replies seem to address tangents to the main question (my impression, anyway):[ul]Would a compression-ignition, gasoline-powered engine work any better than a similar diesel engine?
[li]Would it produce more or less power than the diesel?[/li]
[li]Would it need more or less fuel to produce the same power as the diesel?[/li]
[li]Would it emit more or fewer pollutants?[/li]
[li]What sort of problems does gasoline pose (as opposed to diesel) when used in a diesel-cycle engine?[/ul][/li]
I’ll add a couple of my own tangents:[list=1][li]I’ve heard that by weight, diesel is more energy-dense than gasoline.[/li]
[li]I’m curious, too. Where the heck is that 4-page post on cole, Anthracite?[/list=1]~~Baloo[/li]
[sub]Never mind item 2 – Anthracite read my mind and posted links while I was composing this.[/sub]
These questions are difficult to answer on a general basis. Under a specific example, it is more easy to say. But I will refer to a reference book here for some representative values. Note that others may have somewhat different values or trends (so no calling me a partisan liar yet, OK?).
[QUOTE]
*Originally posted by Baloo * [li]Would it produce more or less power than the diesel?[/li][/QUOTE]
From “Internal Combustion Engine Fundamentals”, John B. Heywood, Co. 1988, McGraw-Hill (damn, I hate it when Grad Reference books still say “Fundamentals”. I mean, WTF?)
From Table 2.1-
“Typical Power per Unit Volume - Passenger Car Spark Ignition Otto Cycle - 20-50 kW/dm[sup]3[/sup]”
“Typical Power per Unit Volume - Trucks Spark Ignition Otto Cycle - 25-30 kW/dm[sup]3[/sup]”
“Typical Power per Unit Volume - Passenger Car Diesel Cycle - 18-22 kW/dm[sup]3[/sup]”
“Typical Power per Unit Volume - Trucks Diesel Cycle (Naturally Aspirated) - 15-22 kW/dm[sup]3[/sup]”
“Typical Power per Unit Volume - Trucks Diesel Cycle (Turbocharged) - 18-26 kW/dm[sup]3[/sup]”
Which in simple terms means gasoline engines produce more power per cubic inch.
[QUOTE] [li]Would it need more or less fuel to produce the same power as the diesel?[/li][/QUOTE]
From “Internal Combustion Engine Fundamentals”, John B. Heywood, Co. 1988, McGraw-Hill
From Table 2.1-
“Approximate best Brake Specific Fuel Consumption, Passenger Car Spark Ignition Otto Cycle - 270 g/kW*hr”
“Approximate best Brake Specific Fuel Consumption, Trucks Spark Ignition Otto Cycle - 300 g/kW*hr”
“Approximate best Brake Specific Fuel Consumption, Passenger Car Diesel Cycle - 250 g/kW*hr”
“Approximate best Brake Specific Fuel Consumption, Trucks Diesel Cycle (Naturally Aspirated) - 210 g/kW*hr”
“Approximate best Brake Specific Fuel Consumption, Trucks Diesel Cycle (Turbocharged) - 200 g/kW*hr”
Which in simple terms means diesel engines require less fuel per unit of energy produced.
[QUOTE] [li]Would it emit more or fewer pollutants?[/li][/QUOTE]
From “Internal Combustion Engine Fundamentals”, John B. Heywood, Co. 1988, McGraw-Hill
Pages 567-577:
[QUOTE] [li]What sort of problems does gasoline pose (as opposed to diesel) when used in a diesel-cycle engine?[/li][/QUOTE]
Without being flippant, mainly that gasoline used in an unmodified conventional diesel engine will spell disaster. It will not work.
[QUOTE] I’ll add a couple of my own tangents:[list=1][li]I’ve heard that by weight, diesel is more energy-dense than gasoline.[/li][/QUOTE]
See my list of fuel higher and lower heating values on a mass basis up above, earlier in this thread. On a mass basis, diesel is not more energy-dense by either measure.
First, NO[sub]x[/sub] out of diesel engines is not comparable to petrol engines, because of the higher cylinder temperatures. And yes, I know I am contradicting the great Heywood.
At any rate, this is before the catalyser. Comparing diesel cars and petrol cars, you may assume that the petrol car is fitted with a cat, since (at least in this country) you can’t buy one without. So NO[sub]x[/sub] concentrations from diesel car exhausts are very much higher than from petrol cars.
First, that’s fine to disagree with Heywood. I said in an earlier thread on power that I disagreed with his opinion on another emissions issue. I’m just surprised that ElvisL1ves has not come by to challenge you to provide proof as to your assertion that the NOx should not be comperable between SI and diesel engines.
And I always assumed we were talking about the “raw” emissions. Since emissions control devices, implementation, and use can vary so much between vehicles, I thought it was best to exclude them from consideration temporarily. But we can discuss those in detail too if you wish.
So in fact, the uncorrected emission of NOx from a diesel engine is on average less than half that from a petrol engine.
This is very surprising (to me at least) because compared to petrol engines, CI engines run both hotter and leaner, both of which favour NOx formation, hence my earlier wrong assumption. It seems this is true even for direct injection diesels.
On the wider question, the study’s authors conclude:
So, on the road diesels produce more NO[sub]x[/sub], much more black smoke, and less CO[sub]2[/sub] than petrol cars.