S. MURALIDHAR

Understanding fuel injection

The days of the carburetor are numbered. After being elbowed out of passenger car engines, the 'carb' is now set to quite literally face the heat from electronic fuel injection even in motorcycle engines. There has been quite a battle on between the top two bike makers - Hero Honda and Bajaj Auto - to beat the other to the market with India's first fuel injected bike. Let us get to understand fuel injection (EFI) technology in the form in which it may be offered in these future two-wheelers.

How does a carburettor work?

The job of a carburetor or an electronic fuel injection system is pretty much similar in that they are both meant to ensure that the engine receives the right amount of fuel and air mixture to promote proper combustion. They differ in their levels of effectiveness while doing this job and the refinement they bring to the process. A carburetor works on the principle of drawing fuel to match the amount of air flowing through a device called a Venturi. Despite advances to the types of carburetors available for use in two-wheelers, including the currently popular constant velocity (CV) carb, this type of injection involves the simplistic sucking in of fuel from an active reserve called the float bowl to be mixed with the incoming air before delivery into the engine. The carb essentially works on the principle of creating intermittent levels of vacuum to ensure constant flow of the air-fuel mix into the engine. Despite the use of a series of fuel circuits to fine-tune the flow of this mixture into the engine and despite the use of other aids such as a throttle sensor, the level of performance improvement that can be squeezed out of a carb is limited.

How does fuel injection own the advantage?

This is where electronic fuel injection technology steps in. While EFI was originally developed for bikes only to enable them to meet more stringent emission norms, it is now clear that as engine size increases, EFI also helps the bike to optimize mileage. Simply put, EFI is a computer-controlled fuel delivery system that enables the independent flow of air and fuel into the engine. The heart of an EFI is the electronic control unit (ECU) that acts as the master command and which sends the requisite instructions to the fuel injectors based on feedback from an army of sensors. The ECU (the on-board computer) is also pre-loaded or pre-programmed with a fuel map with defined injection sequences for varying operating conditions such as idling, coasting and quick acceleration. A number of sensors, including engine rpm, throttle position, ambient air temperature, engine temperature, manifold pressure and crank position sensors, provide constant feedback and information to the ECU regarding the load building on the engine and the other operating conditions. The ECU then uses the information to perform millisecond calculations and then opens or closes the fuel injectors for optimal engine performance to meet the rider's demands and the current operating conditions. The EFI systems that may be offered in the new bikes from Bajaj and Hero Honda may be of two types depending on the kind of sensors they use for gauging the load on the engine. The one that uses a throttle position sensor is called an Alpha N system and the one that uses a manifold absolute pressure (MAP) sensor is called a Speed Density EFI system. Whatever it is that makes it here, one big minus with EFI bikes could be that you will have to forget about getting it serviced by that pavement dwelling mechanic you used to frequent.

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