Hello everyone and welcome. You may notice that diesel vehicles tend to have higher torque figures versus their gasoline counterparts.
So in this video we're going to be talking about five reasons
why diesel engines tend to produce more torque versus gasoline engines,
and we're going to start things off discussing compression ratio.
So if you look at a gasoline engine as that piston is moving towards top dead center as it's moving upward
it's gonna come to a stop sooner versus a diesel engine which is going to continue to compress that air even further.
So why does the diesel engine compress the air more?
Well, this is because the diesel engine is relying on the heat of that air to
instantly combust the fuel as it's injected in so it's raising the air above the self ignition temperature of the diesel fuel
versus in a gasoline engine you're compressing an air & fuel mixture
which you don't want to rise above its self ignition temperature because you want to use a spark plug to ignite it rather than compression.
So the gasoline engine
doesn't compress quite as much to ensure that the temperatures don't get that hot
versus the diesel engine wants that temperature to get really hot so it compresses it even further.
So what does this all translate into? Well by using higher compression ratios
there's a direct correlation between the efficiency of an engine and how much torque it produces so those higher compression ratios
translate into more torque for the diesel engine next we're going to talk about the speed of combustion
so in a gasoline engine a spark as mentioned starts the ignition of that air & fuel mixture
and then the flame travels outward from that spark plug until it finally burns all of that air and fuel,
versus in a diesel engine the fuel nearly instantly combusts as it's injected into the cylinder so complete
combustion occurs much sooner so if you're to look at the Pistons as they're moving
downward the gasoline engine the piston has moved down a significant amount before
complete combustion has occurred verses the diesel engine the piston hasn't moved down quite as much before
complete combustion has occurred and the result means that with the diesel engine there's more time that that fuel is
spending pushing down that piston versus the gasoline engine
which translates into more useful work and more torque produced. So in the gasoline engine
if you still have
combustion occurring when you know the Pistons way down here that combustion is only going to be pressing the piston down for short duration
versus if it happened up top it would have pushed down that piston for the entire duration. So you want that immediate
compression ignition property of the diesel engine to maximize how much torque you produce.
Okay so the third thing we're going to talk about is the bore versus stroke and the fact that diesel engines tend to have a longer
stroke length so if you're looking at a gasoline engine
it's typically going to have a wider bore
but the piston isn't going to travel up and down quite as much
versus looking at a diesel engine, which the piston will travel up and down quite a bit,
but the bore won't be quite as wide as on the gasoline engine. So torque is simply force multiplied by distance
so in the case of a diesel engine you've not only got a larger force,
but you're multiplying that larger force by a larger distance, the distance
rotating around that crankshaft, and so ultimately that's going to translate into more torque produced.
So I've got a simple example here where we've got two engines, which have the same displacement
this is a single cylinder 0.6L
and we've got 120 millimeter stroke on the left with an 80 millimeter bore versus a
100 milliliter bore on the right and an 80 millimeter stroke both of those 0.6L
however, this one has a significantly longer stroke now
I think it's worth mentioning that because combustion occurs much sooner in a diesel engine
it's going to be occurring when it's not at you know the ideal angle for creating that force versus distance
i'm so I'm not
you know totally convinced that stroke length plays all that much of a role in the overall discussion of producing more torque
but it certainly can help to have that greater distance
I think the fact that it has higher compression ratios and that it's
turbocharged are ultimately going to be the biggest driving factors along with that quicker combustion so getting into this a little bit more
part of the reason that this limits a diesel's engine speed is
that the piston has to travel very quickly if the stroke is super long so right here. I've got this example here
where if it's spinning at 3,000 rpm the average piston speed will be 12 m/s,
versus the 80 millimeter stroke is going to be travelling at
4,500 rpm for the piston speed to be traveling an average of 12 m/s so both of these having the same average piston speeds
but this one able to rev up much quicker to a higher rpm without getting into super high piston speeds.
Moving on to number four diesel engines tend to be turbocharged and they tend to be built for turbochargers.
So they are using heavier components iron blocks,
heavy-duty pistons, connecting rods crank shafts, all of this results in a significantly heavier engine
but an engine that is built to be able to handle the increased amount of torque that diesel engines produce
and another thing about diesel engines is that they tend to burn quite lean, so they have a very lean air fuel ratio
18:1 up as high as 70:1 that they can operate in and by burning lean you can have more air to
expand and create more useful work now
that's more an efficiency gain
but also it leads to you know why diesel engines want to be turbocharged to help put in all that air to combine with the
fuel the you know less amount of fuel, but quite a bit of air that you're using to run efficiently
they also don't have the pumping losses associated with
gasoline engines because they'll be throttle less or typically have the throttle
almost always wide open versus gasoline engines
which operate in a much narrower air fuel ratio range
and an overall you know you're not going to see typically as high of boost levels because the engines aren't quite as built
for those higher boost levels that diesel engines are from the factory built for. So again more boost, more fuel,
equals more power and of course more torque and
finally something I think worth mentioning is that the energy density of diesel fuel is greater than
gasoline so if you have the same volume of fuel whether it's a gallon of gasoline or a gallon of diesel
that gallon of diesel is going to have about 10-15% more energy
packed in it than the gasoline so if you're spraying the same volume of fuel into a cylinder that diesel fuel is going to produce more torque.
So thank you all for watching, and if you have any questions or comments, please feel free to leave them below.