I do hear a lot about diesel engines, more specifically how they have to be turbocharged and that they generally have poor acceleration etc. But why is this?
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Diesel is heavier than gasoline… It needs more compression
The engine needs to be bigger, heavier, and is therefore more “sluggish”
The effect is even more visible, if you have them in small European hatchback
I have 1.6 SDI skoda fabia… And it’s awesome car… But you aren’t gonna race with it
Basicly this: Diesel fuel takes longer time to burn.
This means engines cannot opperate at high speed, as a petrol engine would. Furthermore, the “slow burn” also requires robust cylinders etc because of higher pressure., which only adds to weight and overall speed or acceleration.
Turbocharging is obviously going to make it better, but it hasn’t something to do with diesel engines in particular. You can turbocharge most engines.
However, it is pretty common to see a diesel engine to be turbocharged(turbodiesel) simply because it is also more fuel effecient.
Well now that depends on what you mean by underpowered. There’s a reason race cars use gas but big trucks, bulldozers, ships, most tanks, use diesel.
If you want something that speeds up fast to launch you off a starting line, gasoline engines are built lighter as they operate at lower pressures and use a more volatile fuel.
If you want something that runs at a lower speed but at that speed provides much more torque for moving something large at a steady pace, diesel is the right tool.
Try to scale up a gas engine to run something huge? You’re going to have a bad time. Try to scale down a diesel to run something not so huge, like say a passenger sedan? You’re going to have a bad time.
We typically think of “power” as “horse power” in vehicles, which is pretty much rotational force multiplied by rpm.
Gas engines produce less torque (rotational force) then diesels of the same displacement, but can Rev much higher and they get there faster. This is why gas motors feel so peppy and powerful.
Diesel is best for applications where you need actual power over fast response or extream working conditions (high rpm).
My 2.8L I4 diesel has 1/3 the horse power, but nearly the same torque as a 5.3L v8
Diesel engines are like workhorses. They go slower, pull heavy loads and can work a long time. They tend to be heavier.
Gas engines are like racehorses. They accelerate hard and built go fast but have less endurance and don’t do heavy loads very well. They tend to be lighter.
It depends on the application. If you want to run a train, ship or heavy truck – diesel engines are the better option. If you want a lighter vehicle built to carry small loads but can go fast, then petrol engines are better.
Diesel engines work by moving their pistons further than a petrol to squash more air/fuel. This extra distance means the pistons would need to travel further and therefore faster for a given rpm than a petrol limiting the max rpm.
As power is a function of rpm * torque you can see that any cap on rpm will have a negative effect on power.
That said diesels can have pretty reasonable acceleration albeit at the very bottom end of the rev range.
Diesel engines require about very high compression, far more than petrol engines.
To create such high pressures, the piston stroke is a bit longer compared to the piston diameter. To sustain such high pressures, the engine block, head, and crankshaft bearing journals are built much stronger and heavier than in petrol engines.
These factors combine to create an engine that is heavy and rotates more slowly — but which creates far more torque — than a petrol engine.
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