How do diesel engines produce more torque? Even with the same capacity as a gas engine, a diesel engine produces more torque, but how?
If these are some questions intriguing you, then you are at the right place.
How does a car engine work?
Both diesel and gas engines are internal combustion engines, which imply that the fuel and air are mixed inside the engine and this mixture is compressed internally in the cylinders.
Due to compression the fuel gets ignited and pushes the piston inside, rotating the crankshaft which ultimately turns the wheels. The piston then moves outside pushing the burnt gases out from the exhaust.
This cycle is repeated several times per second and the more cylinders an engine has, the more smoothly it runs while it generates more power.
What is Torque?
In physics, torque is defined as a measure of force that can cause an object to rotate on its axis. In simple terms, torque is a twisting force that causes rotatory motion.
In the case of car engines, this rotatory motion leads straight to the wheels. The movement of the wheels is actually caused by the rotatory motion of the pistons in the engine.
In our last segment, we illustrated the difference between diesel engines and gasoline engines. We also explained that the per liter energy content of diesel fuel is 15% more than gasoline.
Now let us see why the diesel engine is torquier then gas engines.
Higher Compression Ratio
The compression ratio is the ratio of maximum volume to the minimum volume inside the cylinder. This ratio is larger in diesel engines meaning that the diesel piston runs up to the very top of the cylinder.
By comparison, in the gasoline engine, the piston stops a bit shorter than the top of the cylinder.
The diesel engine lacks a spark plug and hence the piston runs all the way to the top of the cylinder to close the gap and produces more compression.
High Calorific Value
As mentioned earlier diesel fuel is denser and contains 39.6 MegaJoules/liter of energy compared to 33.7 MegaJoules/liter of gasoline.
This indicates that every time the diesel fuel is burnt more amount of energy is transferred to the pistons thus increasing the torque on the crankshaft.
Stroke Length and Combustion Speed
In the diesel engine, the piston moves to the very top of the cylinder, so the stroke length is longer and as torque equals force multiplied by distance, we have more torque.
In order to combust fuel, diesel engines use air compression and with faster compression rate the fuel burns faster thus adding to torque levels.
The longer strokes of the diesel engine allow the piston to be moved to longer distance thus creating more force or pressure. The more the pressure is built in the cylinders the more torque the wheels get.
Turbo Boost
Diesel engines are turbocharged to make for the lack of horsepower. It increases the amount of air entering the engine meaning more compression inside the engine.
This creates higher pressure in the cylinders, which in turn increase the torque. All modern diesel engines are equipped with turbocharging technology as diesel engines require a healthy amount of air intake.
Diesel turbos are tuned for a much higher boost pressure to reduce pumping losses during the intake stroke that allows the engine to be more efficient in energy conversion.
Mentioned above are a few reasons for the diesel engine to produce more torque than a gasoline engine. However, the main understanding to be taken from all this is that nothing is all-in-all. A gasoline powered engine lacks on torque but makes up it in horsepower.
In a similar manner, the diesel-powered engine will always struggle to rev up in horsepower but compensates for it on torque which may help that potato farmer in Idaho pulling a few tons of potatoes, for instance.
Historically, the diesel engines were designed to move very heavy loads and gas-powered engines were developed for activities that require more power-to-weight ratio, the same reason one never finds diesel engines in supercars.