Monday, July 29, 2013

Carburetion versus Fuel Injection


Dear auto-enthusiasts, Hello again !

In my last article, I had discussed about the components of the Engine (ICE) and how they work in a synchronized way to convert heat energy into mechanical force (Generating Power). During exploring the Otto Cycle, I had told you that its second step is the “Induction Stroke” in which the Charge( Fuel+Air) is sent into the Combustion Chamber of the engine. I assume, most of you already know that the Charge is prepared either by a Carburetor or a Fuel Injection System. Today, I am going to explain that how both of them work, where they are best and where they are not so good. Let’s have a look.

OVERVIEW
To generate power efficiently, the fuel should be mixed with air (oxygen) in such a way that almost all (most of) the fuel present in the Combustion Chamber is burnt and produce maximum possible power without wasting any fuel. This can be achieved by some sort of Carburetion technique, such as a Carburetor or a Fuel Injection System. Whatever the Carburetion technique be, there should be a source of fresh/dust-free air for it. This is achieved by using an air filter. This air is then sent into the Carburetion Module to mix with fuel. The charge so produced is then delivered into the Combustion Chamber through the Intake Valve. Now let us discuss the different Carburetion techniques.
Combustion Chamber
WHAT IS CARBURETION ??
Carburetor

The first word that you might think of while reading this section would surely be a “Carburetor”.
Yes, carburetor is one way of carburetion but it is not the only way. Actually, Carburetion means the process of mixing fuel with a suitable amount of air to make a stochiometric mixture which can be completely burnt. So, be it any method, using a carburetor or a fuel injection system, it will be called as carburetion.

There have been various techniques that have been adopted for carburetion in past, but the most common methods that are currently used are Carburetors and Fuel Injection Systems. These systems can also be sub-classified.

CARBURETOR:-
Carburetor is the most common Carburetion equipment in small capacity motorcycles and many modified cars. They are cheap to manufacture and can be tuned to obtain maximum power at low cost. A carburetor consists of 4 to 5 different fuel circuits to create the Charge based on different positions of the throttle(accelerator) and load on the engine. These circuits consists of different type of fuel jets, namely:
Carburetor Main Jet
  1.       Main jet.
  2.      Pilot jet. 
  3.      Jet needle. 
  4.      Needle jet. 
  5.      Slow jet or Air/fuel-screw.
These jets are of different sizes and they open up at different requirements of engine, such as, high load or wide-open throttle conditions.

There are many different types of carburetors depending on the usage, for example, down-draft and up-draft carburetors were used in Aircrafts(rarely used now) while side-draft carburetors are used in Automobiles. In some cases, a carburetor is used with a fuel pump which is often called a pressure carburetor. It is considered as an early form of Fuel injection.

ADVANTAGES:-
  1.       They are cheap to manufacture. 
  2.       No complex electricals are involved. 
  3.       Good for engine tuning and low budget performance modifications. 
  4.       No fuel pump is required.

DISADVANTAGES:-
  1.     Not very fuel efficient. 
  2.      Many harmful gases are evolved as it is not very precise.
  3.      To fully exploit its capabilities, a great deal of experience is required. 
  4.      It is dependent on atmospheric pressure for working, which is not the same at places situated at different altitudes. So, jet replacement is required every time one moves to a different altitude.

FUEL INJECTION SYSTEM:-
Fuel Injector

Fuel injection Systems are less common in small capacity motorcycles but they are widely used in large capacity motorcycles and almost all production cars at present due to the fuel efficiency benefits and harder emission regulation standards. They use highly advanced electronic sensors such as Oxygen sensor, Intake Manifold Pressure sensor, Crank Angle sensor, Fuel Pressure sensor and Throttle position sensor to calculate the correct amount of fuel to be delivered for any situation like high load or high power requirements. They also use a fuel pump to create pressure in the fuel injector nozzle, pressure regulator to provide the right pressure required for any required situation and an ECU(Engine Control Unit) to control all these electronics as well as the Ignition of spark plug(s), if any.

They can be of many types, of which can be classified as Direct Injection, Multi-point Injection or Manifold Injection depending on the type/location of Fuel Injector(s), Closed-loop or Open-loop depending on the inclusion/exclusion of Oxygen and Manifold Pressure sensor and Programmable or Non-Programmable depending on the ROM chip used in the ECU.
Fuel Injection

ADVANTAGES

1. They are very fuel efficient.
2. They are very precise, so very less amount of harmful gases are evolved during combustion.
3. Some highly advanced and fully-programmable Fuel Injection Systems can be used to exploit the full potential of an engine, just by using some programming software installed in a laptop.
4. It uses an intake manifold pressure sensor, so it can automatically alter the fuel delivery according to the atmospheric pressure(different altitudes)

DISADVANTAGES

1. They are very costly as compared to carburetors.
2. A lot of complex electricals are involved, which makes it very difficult to repair.
3. A fuel pump is required for it.
4. Every thing in it depends on electricity. So in case of a battery failure, the vehicle will be unable to start at all.

I hope that you guys understood and enjoyed the article. I will come up with more technical articles in coming days.

-Article by Ishan Dev