Richard Smith wrote on 5/30/2022 5:57 AM:
> Hi all
>
> On this bright morning I thought to ask you here on r.c.m. if any of
> you know what makes the difference for a diesel car between very good
> fuel consumption and just good fuel consumption.
I am not a regular in this newsgroup but I once owned a VW Jetta TDI,
and I think I am knowledgeable enough on this matter to answer your
question.
Diesel fuel has higher "energy density" than regular gasoline (or
petroleum in the UK). In the oil distillation process in the oil
refinery, diesel fuel is less refined than regular gasoline, and thus
contains more complex hydrocarbon molecules than regular gasoline.
Theoretical a tank of diesel fuel contains more heat energy than the
same volume of regular gasoline if you can burn the fuel thoroughly
through proper combustion.
A diesel engine does not use a spark plug to ignite the fuel in each
combustion cycle. Instead it uses high compression to ignite the
air-diesel mixture, therefore a diesel engine requires stronger metal
components, and thus lasts longer and costs more money to build.
Another advantage of using diesel is that diesel is technically
equivalent to Jet A1 fuel + motor oil. Jet A1 fuel is a common aircraft
engine fuel which is basically a fancy type of kerosene. Because the
less-refined diesel fuel has the engine oil built into it, it actually
lubricates the combustion chamber in each stroke.
With the combined effect of better metal components in building a diesel
engine, a higher energy density of diesel fuel compared to regular
gasoline, and the innate lubricating power of diesel fuel itself, a
diesel engine is renowned to have better fuel economy and last longer.
The disadvantage of using diesel engine in a car is that a diesel engine
is more sluggish in picking up speed compared to a gasoline engine. If
you want jack-rabbit starts after each red traffic light, then a diesel
car will disappoint you.
Diesel engines are the preferred choice for vehicles that require fuel
economy and engine durability. That's why commercial trucks are almost
exclusively diesel.
Hope that helps.