In message , Dave Plowman
writes

Showing just how inefficient a petrol engine is.

Perhaps you'd better set about a more efficient way of converting a
high density fuel like petrol to mechanical energy, then. Electric
vehicles driven off storage batteries have been around for nearly as
long. If they were capable of being developed into a viable competitor,
it would have been done years ago.
Try diesel. Or indeed any compression ignition engine.
--
Clive

"Clive" wrote in message
...
In message , Dave Plowman
writes

Showing just how inefficient a petrol engine is.

Perhaps you'd better set about a more efficient way of converting a
high density fuel like petrol to mechanical energy, then. Electric
vehicles driven off storage batteries have been around for nearly as
long. If they were capable of being developed into a viable competitor,
it would have been done years ago.
Try diesel. Or indeed any compression ignition engine.

I've always wondered: is it the fact that diesel engines use compression
ignition or the fact that they use different fuel which gives rise their
greater efficiency and their greater torque at lower engine revs?

In message m, Martin
Underwood writes

I've always wondered: is it the fact that diesel engines use
compression ignition or the fact that they use different fuel which
gives rise their greater efficiency and their greater torque at lower
engine revs?
Higher compression makes them more efficient, further as a petrol engine
throttles back the compression drops even more making them more
inefficient. I think the only thing in a petrol engines favour is it's
quietness at idle, caused by low compression and therefore
correspondingly lower flame propagation speed.
--
Clive

"Clive" wrote in message
...
In message m, Martin
Underwood writes

I've always wondered: is it the fact that diesel engines use
compression ignition or the fact that they use different fuel which
gives rise their greater efficiency and their greater torque at lower
engine revs?
Higher compression makes them more efficient, further as a petrol engine
throttles back the compression drops even more making them more
inefficient. I think the only thing in a petrol engines favour is it's
quietness at idle, caused by low compression and therefore
correspondingly lower flame propagation speed.

Why should the compression of a petrol engine vary with throttle position?
Surely compression ratio is determined simply by the ratio of the volume of
the cylinder with the piston at the top of its travel to the volume with the
piston at the bottom of its travel. Or am I missing something very obvious?

Why were high-compression-ratio petrol engines and 5-Star petrol phased out?
I can remember in the 1970s, many makes of car had a top-of-the-range model
with a high-compression engine. Was more energy/pollution generated in
refining higher-octane petrol - was that what spelled the death-knell of
those engines? From what you are saying, high-compression engines would
presumably have been more efficient to run. However I presume
higher-compression petrol engines had a greater tendency for compression
ignition (pinking) to occur accidentally.

Is there a trend to run modern petrol engines at higher rpm (ie
lower-geared) that there used to be? My Mark 2 Golf (1800 non-injected
engine) was certainly higher-geared (mph/rpm) than my Mark 3 Golf (1800
injected engine) and had a greater acceleration, especially 50-70, though it
may have been a lighter car so its power or torque to weight ratio would
have been higher.

In message m, Martin
Underwood writes

Why should the compression of a petrol engine vary with throttle
position? Surely compression ratio is determined simply by the ratio of
the volume of the cylinder with the piston at the top of its travel to
the volume with the piston at the bottom of its travel. Or am I missing
something very obvious?

Why were high-compression-ratio petrol engines and 5-Star petrol phased
out? I can remember in the 1970s, many makes of car had a
top-of-the-range model with a high-compression engine.
A butterfly valve controls the flow of air in a petrol engine to keep
the air fuel mixture correct, thus causing a depression on the inlet
side. This is often used to power servo brakes.
I believe 5 star was phased out because of it's high lead content.
--
Clive

In article m,
Martin Underwood wrote:
Why should the compression of a petrol engine vary with throttle
position? Surely compression ratio is determined simply by the ratio of
the volume of the cylinder with the piston at the top of its travel to
the volume with the piston at the bottom of its travel. Or am I missing
something very obvious?

It's the actual pressure caused by compression that's important, and a
throttle causes a partial vacuum - so compressing air at less than
atmospheric pressure gives a lower final pressure. Similarly, using a
supercharger etc increases 'atmospheric' pressure and the final compressed
pressure. If you could develop a supercharger which was super efficient,
you could negate the effect of the throttle.

--
*It was all so different before everything changed.

Dave Plowman London SW 12
RIP Acorn

In message , Dave Plowman
writes
Similarly, using a supercharger etc increases 'atmospheric' pressure
and the final compressed pressure. If you could develop a supercharger
which was super efficient, you could negate the effect of the throttle.
But you'd then have to adjust the fuel accordingly which would mean the
engine accelerating uncontrollably until it burst. One thing
overlooked with petrol and diesel (or steam) is that all reciprocating
engines have nil torque at TDC and because modern diesels have up to
five bursts of fuel between TDC for ignition and 90 degree after TDC
maximum torque, diesels will always win hands down. I find a lot of
people equate engine power with bhp and don't take torque into account,
hence a PP who was witering on about F1 engines.
--
Clive

In article ,
Clive wrote:
I find a lot of people equate engine power with bhp and don't take
torque into account, hence a PP who was witering on about F1 engines.

BHP is the product of torque and rpm. An ideal engine might have the peak
torque and maximum BHP as widely separated, rpm wise, as possible.

--
*I get enough exercise just pushing my luck.

Dave Plowman London SW 12
RIP Acorn

Clive wrote:

I've always wondered: is it the fact that diesel engines use
compression ignition or the fact that they use different fuel which
gives rise their greater efficiency and their greater torque at lower
engine revs?
Higher compression makes them more efficient, further as a petrol engine
throttles back the compression drops even more making them more
inefficient. I think the only thing in a petrol engines favour is it's
quietness at idle, caused by low compression and therefore
correspondingly lower flame propagation speed.

Sorry , I disagree. The only thing in diesels favour is its lower
fuel consumption. Thats it. Diesels max rpm are limited by the physical
characterstics of the fuel , which results in a lower max power for a given
engine size than a petrol engine (when was the last time you saw 15,000
rpm diesel motorbike engine or a diesel F1 car?) , their throttle response
frankly is rubbish in comparison , they're heavier and the combustion process
at full power is a mess (how many times have you seen even a new diesel vehicle
belching out black soot) and because of this they can't use catalytic
converters and to get any reasonable power out of a diesel you have to shove
on an expensive turbo. Yes diesels put out more torque than a petrol engine of
equiv size but thats easily solved by different gearing on the petrol. The lack
of power however can't be solved by gearing.

To be honest diesel engines are a prehistoric bit of kit which belong alongside
steam engines in a museum and which only still exist because of their
*slightly* higher fuel efficiency than petrol (and if
you measure it by weight of fuel used and not volume the story isn't so rosy
for diesel as you'd imagine) and slightly less maintence. If diesel prices were
to rise relative to petrol the diesel car (and possibly other vehicles) would
soon vanish off the roads and the sooner the better IMO.

B2003

In message ,
writes

Sorry , I disagree. The only thing in diesels favour is its lower fuel
consumption. Thats it. Diesels max rpm are limited by the physical
characterstics of the fuel , which results in a lower max power for a
given engine size than a petrol engine (when was the last time you saw
15,000 rpm diesel motorbike engine or a diesel F1 car?) , their
throttle response frankly is rubbish in comparison , they're heavier
and the combustion process at full power is a mess (how many times have
you seen even a new diesel vehicle belching out black soot) and because
of this they can't use catalytic converters and to get any reasonable
power out of a diesel you have to shove on an expensive turbo. Yes
diesels put out more torque than a petrol engine of equiv size but
thats easily solved by different gearing on the petrol. The lack of
power however can't be solved by gearing.

To be honest diesel engines are a prehistoric bit of kit which belong
alongside steam engines in a museum and which only still exist because
of their *slightly* higher fuel efficiency than petrol (and if you
measure it by weight of fuel used and not volume the story isn't so
rosy for diesel as you'd imagine) and slightly less maintence. If
diesel prices were to rise relative to petrol the diesel car (and
possibly other vehicles) would soon vanish off the roads and the sooner
the better IMO.

B2003
I sometimes try trolling, but at least I'm honest about it, and I know a
few facts before I start, the rubbish above shows just how little you
know about the different fuelling systems in current use on just cars
alone.
--
Clive