Diesel engines are among the most efficient engines in the market. Well, multiple factors are making them lead the fuel efficiency charts. On the contrary, diesel engines are heavy but are reliable, they are less powerful but have excellent torque figures. Additionally, these diesel guzzlers do have a separate fan following. Keeping that in mind, for those who wonder how the diesel engine does what it does the best, let’s have a look. In today’s feature, we will look into a little detail of what goes behind the diesel injection in these long-stroke engines.
Before getting started, let’s have a glimpse of what is diesel injection.
Diesel Fuel Injection
To begin with, be it a diesel engine or a petrol engine, the majority of the engines follow 4 strokes to generate power. Intake stroke, Compression Stroke, Power stroke and in the end exhaust stroke.
- In the case of the diesel engine, it is the time in between the compression and power stroke when the fuel is injected into the combustion chamber.
- Talking further, in these high compression engines, it is just the fuel that is injected into the combustion chamber.
- Dissimilar to the petrol engine, the injectors atomize the fuel at very high pressure inside the diesel engine. Depending upon the engine, it may vary from 10,000psi to 30,000psi.
Fun Fact: In diesel engines, the throttle pedal controls the amount of diesel getting atomized into the chamber. Meaning, depressing the throttle, will increase the amount of fuel being sprayed. And this is how we are able to accelerate a diesel-powered vehicle.
Now, the main purpose of the injection system is to stoichiometrically deliver the fuel inside the engine. But the way it is delivered does make a lot of difference in the engine efficiency and performance.
Types of Diesel Injection
So, the automotive industry is forever gaining pace making the engine, more refined, powerful and efficient. A part of the credit also goes to the fuel, here the diesel injection system. Now diving into utmost detail, the diesel injection system can be classified into 2 types, Direct Injection and Indirect injection.
Unlike the petrol engine, a diesel engine does not require a spark plug to ignite the air-fuel mixture. Because the diesel fuel has a lower self-ignition temperature, it ignites when the pressure increases which in turn heats up the situation. Meaning, the temperature rises inside the combustion chamber, igniting the fuel.
- Majorly in an indirect injection system, the injector sprays the fuel in a separate compartment called the prechamber. And in this prechamber, a glow plug is also mounted that heats the area during cold starts.
- Now, the diesel injector inside the prechamber injects the fuel. Next, because of the swirl motion caused by the piston’s movement the heated diesel mixes with the air forming the charge.
- Later as the piston further compresses the charge, it ignites due to the increase in pressure and temperature.
Direct Injection (DI)
Moving to modern technology, it is the direct injection that is used in many vehicles in this current era.
- Okay, why this is used, you may ask? Well, the injectors spray the diesel fuel directly inside the combustion chamber.
- And no, no special glow plug is required as the cooling surface of the cylinder is fairly small.
- This allows better control over the fuel delivery inside the engine. Because of this, it is only the air that enters the chamber through the intake valve and permits a better air-fuel mixture.
- And in the end, this well-mixed charge allows for better and more efficient combustion. The advantage of direct injection is better thermal efficiency and better cold start properties.
- Talking about the diesel injection pressure, it is the fuel pump that regulates the pressure of injection.
Common Rail Direct Injection (CRDI)
Now, a type of direct injection is the common rail direct injection system. Like in the DI, the injectors the CRDI also atomize the diesel fuel straight into the combustion chamber. Also, the working and the injection timing is similar to that of the DI system.
- The difference lies in the fuel lines of the injectors. In the DI, the injectors are straight connected to the fuel pump that regulates the pressure and the amount of diesel being injected into the chamber.
- On the contrary, in CRDI all the injectors are connected with a common rail that receives the flow of the fuel from the fuel pump.
- There it is the common rail that regulates the pressure and the amount of diesel being injected. The advantage of CRDI is that here we have better control over the injection than in the DI. This means the engine runs more efficiently.
Hyundai is among the companies that use CRDi technology in their diesel engines.
Interesting read: 10 Most Affordable Diesel Automatic Cars In India