why diesel engines are having hight torque comparing with the same size of Petrol Engines ??
yunust...@gmail.com
Well , im trying to have your opinons buddies , im doing a small search
bout this subject . so anyhelp . i got a lot of stuff but still
wondering how the torque can have direct effect on the engine .
waiting al ur replies .
10x advance ,
SnoMan
THere is a couple of reasons. THe first ishow the energy is extracted
from fuel in that it has very high compresion (16 or 18 to one or
better) which increases the amount of power extracted. Next there is
how the fuel purns more slowly with a lower expansion cycle which asle
extract more energy over a lower period of crank rotation. (it also
greatly limits the efective RPM of engine too) Last and most
importantly, there is the boost as modern diesel run between about 17
and 30 PSI boost which increases effective displacement. Example, a
400 cu inch motor running about 15 lb of boost uses the same amount of
air as a 800 cu in motor without it and a 800 cu gas motor would have
awesome torque. Take away the boost from a CTD, a PS or a Dmax and it
would be pretty gutless. By same token run the same amout of boost on
a gas engine and the power would be downright scarey at times. The
main reason that you do not see boosted gas motor is the publics
affinity for 87 octane fuel which would destroy a gas motor when
boosted. Had it not been for high performance super and/or turbo
charged gas engines that powered allied aircraft in WW2, the world
would be a different place today. Also had it not been for germany's
affinty for diesel tanks , the russain front battle may have gone
differently because they soon found them to be next to useless in
really cold weather. True, the fuel was less volitule in combat damage
but it did not much matter if it will not run. There is pluses and
minuses to both engine types but cu in for cu in, a gas motor will
make far more HP power than any diesel will at the same relative
manifold pressure. Witha 400 cu gas motr you can easily make 300HP
with no boost plus but same size diesel with out boost might make 160
or so if you are lucky. To compare engines effectively, you need to
consider tha amount of air they use because as stated earlier, boost
changes its "effective" displacement. too. Furthermore if you design a
gas engine from scratch to run on better fuel than 87 octane you can
increase CR a lot and boost output and efficency as well. 87 octane is
more of a hinderance to gas engine efficency than most people want to
except because were it not for it, we would have main stream engine
with 11 and 12 to 1 CR like we did in 60's and better power and use
less fuel doing it too.
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TheSnoMan.com
Lon
Check the compression ratio and peak combustion pressure on a diesel and
a typical gasoline engine.
Doug
to shift down to get the power you need. Look at the rock crawlers,
they have gears so low they can go 1 mph at 5000 rpm! Power is what you
need. Torquey motors give good power at low rpms, which is a kick I
guess.
Diesel fuel has more btus (watts) per gallon than gasoline. Diesels
engines can be run at higher compression ratios because engines wont
ping with the diesel fuel. I think just about all diesel engines are
fuel injected (but so are gas now). Anyway, both work. Personally I
don't like the noisy, dirty, stinky diesel (prefer gasoline), but they
do work well. Make an engine with really big cylinders and big flywheel
and you will have a torqy sob no mater what fuel you use.
SnoMan
wrote:
>Diesel fuel has more btus (watts) per gallon than gasoline. Diesels
>engines can be run at higher compression ratios because engines wont
>ping with the diesel fuel. I think just about all diesel engines are
>fuel injected (but so are gas now). Anyway, both work. Personally I
>don't like the noisy, dirty, stinky diesel (prefer gasoline), but they
>do work well. Make an engine with really big cylinders and big flywheel
>and you will have a torqy sob no mater what fuel you use.
Actually diesels ?ping/knock" all the time, that is where noise comes
from. while there is about a 12% difference in BTU content the biggest
thing limiting gas engine power and efficency is low octane fuel
because there are those that think 87 octane is the wonder fuel which
it is not and detriot has to do a LOT of trickery with timing curves
and CR ratios to control knock from it which reduces power and MPG. In
the 60's and early 70's you knew when you were not feeding your engine
right because it would knock big time but today they mask it with
knock control that quietly steals your power from you.
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TheSnoMan.com
Lon
High pressure direct cylinder injection appears to be giving a lot of
the benefits of diesel in gas engines.
Willem-Jan Markerink
@m73g2000cwd.googlegroups.com:
Even *if* you have a slushbox with high stall-ratio, you *will* have to put
your high-power/low-torque engine through that gutless range from idle to
peak-power.
Or do you jam your slushbox into Drive after you revved up the engine?....:))
--
Bye,
Willem-Jan Markerink
The desire to understand
is sometimes far less intelligent than
the inability to understand
<w.j.ma...@a1.nl>
[note: 'a-one' & 'en-el'!]
SnoMan
wrote:
>High pressure direct cylinder injection appears to be giving a lot of
>the benefits of diesel in gas engines.
It holds a lot of promise because it eliminates fuel being lost during
scanvanging which improves MPG and also allows for higher CR ratios
for a given fuel octane because the injection of fuel into cylinder
just before ignition cools the mixture as fuel vaporizes rahter than
being lost to intake port walls and such and higher CR ratio ment
better power and MPG too. In theory you could run about 13 to 1 CR
with a gas motor with direct injection and 94 octane and get a nice
power and MPG boost too. I look for DI on gas engines to be main
stream by 2010and for diesel to start loosing their luster after that
because the MPG difference will be a lot less and the diesel will
still cost a lot more to buy and fuel. DI will alos make it easier to
supercharge gas motors too.
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TheSnoMan.com
Doug
units). If your torque is in ft. lbs and you multiply by the rpm of the
engine, you get your horsepower. You can look at the torque curves and
horsepower curves for engines in car magazines that review the cars.
When people talk about an engine that "has a lot of torque" what they
mean, usually, is that it has a lot of torque at low rpm.
The design of the engine, the bore and stroke and size of the pistons
and weight and size of the crank and flywheel all play a part in how
much torque and horsepower an engine has. I don't really think that a
diesel engine has more torque by being a diesel. It's just that these
are usually truck engines and they want it to have good pull at lower
rpm, so they make it so it has good torque at low rpm. However, I'm no
expert.
SnoMan
wrote:
>Horsepower is torque times speed (and maybe a constant to get the right
>units). If your torque is in ft. lbs and you multiply by the rpm of the
>engine, you get your horsepower. You can look at the torque curves and
>horsepower curves for engines in car magazines that review the cars.
>
>When people talk about an engine that "has a lot of torque" what they
>mean, usually, is that it has a lot of torque at low rpm.
>
>The design of the engine, the bore and stroke and size of the pistons
>and weight and size of the crank and flywheel all play a part in how
>much torque and horsepower an engine has. I don't really think that a
>diesel engine has more torque by being a diesel. It's just that these
>are usually truck engines and they want it to have good pull at lower
>rpm, so they make it so it has good torque at low rpm. However, I'm no
>expert.
>
The burning properties of diesel fuel developes good low RPM power but
it has its limitations and with proper gearing a gas motor can do a
fine job. Most gas motors are just getting started when oil burners
are running out of breath and if you gear a gas motor a lot
differently than a deisel to use its power curve properly it will pull
well. Most do not because people have a mental block on what a good
axle ratio is for a gas motor and gear them wrong. BTW, 600 ft lbs of
torque at 2000 RPM is the same HP as 450 ft lbs at 3000 or 300 ft lbs
at 4000 RPM. Als remeber that a diesel needs a lot more size to exceed
the torque output of a gas motor either via more displacement or
boosting with increases its effective displacement. Take the turbo of
a CTD, PS or Dmax and it will be quite gutless.
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TheSnoMan.com
Jon R. Pickens
it makes peak power (horsepower) at 5100rpm. It's practically useless
in that truck. Sure, it can make power, but only at such a high rpm
that it'd be screaming down the road. Even with 3.73 gears and 31"
tires, I only turn around 2000rpm at 80mph.
The truck would run much better if it made it's peak torque at a much
lower engine speed. I would not have to turn it as fast. As it stands
now, there's no low-end acceleration, it runs incredibly rich at low
speeds, and the gas mileage is horrendous (11mpg on the interstate).
Horsepower is a derived value...it's not measured, it's determined.
It's used to describe how much work is done over a period of time. The
truth is, I have no need for that much "work" to be done in that short
of a time period. I need torque, and lots of it, and will need even
more once the lift kit is installed with the bigger tires.
Horsepower could not be any more irrelevant to me than it is right now.
Buying into the idea of more HP for the money is what got me into this
mess with my truck.
~jp
Willem-Jan Markerink
4ax.com:
Do you or anyone else have more data-samples on CR vs octane rating,
divided into the category 'carburator', 'injection' & 'direct-injection'?
(there is no octane-limit difference between carburator & injection I
believe, but I would like to see more samples about DI)
(I bet you could at least theoretically calculate the thermical gain of the
injection/evaporation, but since the octane rating has no real math behind
it (other than laboratory samples giving a certain mixture of the chemicals
octane vs heptane), you can't calculate much without a table with field-
data....
(at least based on carburator-CR vs octane rating)
SnoMan
<w.j.ma...@a1.nl> wrote:
From what I have seen and read DI with a gas engine decreases the
octane requirement on a engine at any given CR. The reason for this is
that DI cools the mixture at the time of injection as the gas
vaporizes before ingition. These cooler temps reduce tendancy of fuel
to preignite and retards knock. With a carb,TBI or mulitpoint the
mixuter is heated by intake or head ports before it is even
compressed. Furthermore the high injection pressures required for DI
better atomizes the fuel and more completely mixes it with air in
chamber and because fuel is injected before ignition but after valves
close there is no loss of mixture to valve overlap so a more
aggressive profile can be used too. Together with higher CR which
boosts voluetric efficency and less fuel loss because of design, you
will see a net gain of about 10% more HP and about 10 to 15% better
enconomy too and lower HC emissions too. DI for a gas engine is long
overdue.
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TheSnoMan.com
Willem-Jan Markerink
news:cg07r2tj4fa24229v...@4ax.com:
Yesyes, but I would like to see a quantification/math of the gain in *octane*
rate, when changing to DI....:))
Casus:
Engine: Volvo C3-series with a Volvo B30A carburated gasoline, and a CR of
9.3:1, requiring 98 octane (a different version, B30F, with CR of 8.7:1,
accepts 91 octane, by having a 3mm thicker head gasket (meant for lousy
(marine-grade) fuel)).
Fuel: in Siberia en Mongolia it goes down to 76 and even 72 octane....:))
(and that was the *main* route, from west to east, and north to south....a
red line on the map....but hardly any line in the sand, not even always 2
vehicles wide on asphalt....:))
(these C3-series are so low geared (5.9/7.1/7.6:1) that a diesel-conversion
doesn't make much sense, neither (overall) cost-wise nor fuel-wise (since
only modern diesels achieve the necessary rpm, and modern diesels don't like
the lousy quality of diesel in those area's either (there is only one high-
revving diesel on the market that doesn't care much about fuel quality, and
that is the Steyr M1, both 6 and 4 cylinders (both also used/produced under
license in east-block countries, for the same reason)....but alas, it is too
new to be available as cheap surplus/donor component)
Yes, I know DI isn't an easy modification by any stretch of the imagination,
but I would at least *theoretically* like to know what the gain is....:))
Even even 72 octane comes into the realm of this engine, then it might be
worth the effort....:))
Even just a few data-samples of any comparable engine would be nice to know
(like different generation of the same block/CR for old&new cq TBI/DI).
Or: what would your above 13:1 CR (then 94 octane) have required *without*
DI?
Thanx!....:))
SnoMan
<w.j.ma...@a1.nl> wrote:
>Yesyes, but I would like to see a quantification/math of the gain in *octane*
>rate, when changing to DI....:))
That would be kinda hard to do because there are a lot of varibles
involved. for instance, chamber size and shape, piston shape, bore to
stroke ratio and engine displacement. (the smaller the bore relative
to cylinder dispalcement, the more heat loss there is to cylinder
wall, head and piston because the ratio of volume to surface is not
constant and the more surface area there is, the more it will tend to
quench the knock that can develop because it keeps mixture from hot
spoting. I have seen data to suggest that DI will allow you to raise
CR about 1 to 1.5 points with same octane but again there is no hard
fast rule that would apply to all engine configurations. Sorry that I
can not provide a hard fast rule because a "simple equation" does not
exist. Most engine made today are well beyond 87 octane it true
requirement but the knock control systems they use to retard spark to
mask it does a good job and keeps consumers happy while stealing
efficency and power in the process.
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TheSnoMan.com
Lon
Any particular engines claimed to be rated for 87 octane that really
need higher?
SnoMan
wrote:
>Any particular engines claimed to be rated for 87 octane that really
>need higher?
Basically any engine running a CR of 8.5 or hogher needs more than 87
octane and require active knock control in the form of spark
management and EGR (EGR is used to lower peak combustion temps for
reduced NOx emissions and it also dilutes mixuture and retards burning
rate which limits knock) The problem is that when you use these
methods (especailly spark control) you reduce peak pressures and and
change the crank angle at which thiese peaks are reach and therefore
reduce the efficencny of the IC engine. Also to further complicate the
problem, true octane requirement of a engine are not constant so you
need to pick a octane grade that is high enough to cover peak needs.
Also modern engine tend to need less octane at higher RPM's (say above
3500 to 4000 RPM) because the the cylinder volume is expanding so
quickly that it is less prone to detonate that and they use a timing
curve at WOT that is not very aggressive either to better tolerate
lower octane fuel to keep consumers happy. At lower RPM's octane
requirement tend to increase because of slower expansion rates so more
sprak control is needed which effects responce and MPG in town,
especailly on hot days with A/C on. Furthermore engine load,
altitude, tempature and humidity also plays a role too. This is why a
modern engine may run like a bandit on 87 octane when it is cold and
damp because less octane is needed then and suck in hot temps and lack
power towing with 87. Back in the old days, there was no mystery as to
want octane you engine needed because they where tuned for peak power
not to tolerate low octane fuel and if you did not feed it properly,
you heard it and so could everyone else around you in traffic. As I
have said before, active knock control via spark retarding serves no
purpose in emission controls, it is there to limit consumer complaints
while they satisfy their desire to by the cheapest fuel they can. To
be truthfull and even suggest that your car really needs more than 87
octane in the manual is a death sentance for sales unless all car
manufactures did it because the one that did not would play up that
their vehicle do not need higher octane fuel. Consider this too, when
87 octane came out in the early 70's engine designed to run on it had
8 to 8.5 to one CR max and it was only after the introduction of sprak
trickery that they were able to raise it higher in later years. They
also run all EPA MPG test with 93 octane fuel, never with 87 octane.
One reason Dodge had so much trouble with V10 in trucks was poor knock
control and people running 87 octane towing with them which would have
a tendancy to ping (even if below audiable level) and the vibrations
from this pinging causes the valve to vibrate in seats and leak which
leads to erosion and a eventual burned valve. Most do not realize how
detrimental knock can be to valves over a period of time because it
can do more than damage pistons and heads. (it takes a severe knock to
damage pistons and such but a lot less to damage valves over time)
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TheSnoMan.com