Thursday, August 20

Carburetors vs. Fuel Injection

Carburetors vs. Fuel Injection
By: Nick Fugate

    Carburetors have been used on engines since 1882 when Enrico Bernardi developed one for his one cylinder prototype engine.  The carburetor is the oldest method of air fuel induction. The correct mixture of gas and air results in a smooth running engine. This can be a tricky process considering each engines preference for fuel. This is where the specifics of the parts come into play.

    Carburetors contain a venturi, a throttle, a metering rod or fuel tube, a float chamber, and a choke. The flow of air through the venturi causes a pressure drop which pulls fuel through the metering rods and into the air stream. The flow of fuel is controlled by the pressure and the nozzle on the rod along with the atmospheric pressure in the float chamber. The volume of the pressure drop then controls the operation of the engine, which responds to the position of the throttle. 

    The choke controls how much air flows through the carburetor. When the choke is closed, the amount of airflow is limited causing a fuel-rich mixture to flow into the engine cylinders. This process is needed when starting a cold engine.

    Carburetors were regularly used until the mid 1980’s when fuel injection was introduced. Fuel injection offers better fuel economy and a broader power curve. A fuel injector is nothing more then an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump and is capable of opening and closing many times per second. When the injector is energized an electromagnet moves a plunger that opens the valve and allows the pressurized fuel to squirt out through a tiny nozzle. This atomized fuel improves combustion. The finer the mist the more easily the fuel burns. The injectors are mounted in the intake manifolds so that they spray fuel directly at the intake valves. The fuel rail supplies pressurized fuel to all of the injectors. There are three basic types of fuel injection; throttle body, multi-port (batch fire), and sequential system (fires one at a time).

    When purchasing a new boat be sure to inspect the engine and see what system is being used in the boat. With the pros and cons of each system one must decide which is more economical for their purpose.