Open Loop Fuel Injection System:
To understand this concept properly, imagine a simple loop of anything really. A loop is something which has a same starting point and the same ending point and the cycle keeps going on and on in a never ending state. This is what a loop is, pretty much a never ending cycle. Now when we put this in terms of Fuel Injection systems of motorcycles it means the loop is open, i.e. the loop has an end somewhere and there is no acknowledgement of the process.
READ ALSO: Motorcycle Fuel Injection (Fi) System Explained
So in an open loop FI system, the air fuel mixture goes into the combustion chamber, it ignites, power is generated, the exhaust gases exit the chamber and that’s that. All good for now; but when this cycle ends, unlike in closed loop FI system which we will come to in some, there is no acknowledgement back to the ECU. This is what happens in a factory fitted single mapping FI system. The preset factory setting is what the bike runs on and this is the system found in the entry level and middle-weight sports bikes like the KTM Duke and RC 200 and 390. Here the outside conditions do not matter to the bike and the FI system just simply works the way it is programmed to and nothing else. Closed Loop Fuel Injection System:
In this FI system, there is an Oxygen sensor or an O2 sensor located inside the exhaust system of the bike. This sensor records the contents of the gas that is exiting the bike. So in case the gas has a high amount of oxygen content in it, then it means the bike is running lean, while if the oxygen sensor is indicating very less or no amount of oxygen in the gas, means the bike is running rich.
With fuel delivery systems it is always about hitting that 14.x/1 ratio. I.e. for every 1 part of fuel, there should be 14.x parts of air. Now this “x” value keeps on changing depending upon a lot of factors like atmospheric temperature, pressure, air density, oxygen levels in the air, pollution levels in the air, etc. Sometimes this figure even varies up to 12 for a very rich mixture or else to 14.8 for a very lean mixture. Most of the times the ideal range is of about 14.0-14.3 for the best fuel efficiency as well as optimal power generation to give the bike the performance it is meant for.
READ ALSO: Carburetor Vs Fuel Injection- Motorcycle Fuel Systems
So in case of the closed loop Fi system, the oxygen sensor picks up the readings and relays it to the ECU and the ECU then according to the readings adapts the fuel injection levels to get the best result out of the bike. This process happens pretty much multiple times in every second and hence this type of FI units are used in all the top notch bikes which rely on precision as well and not only on pure power generation. One has to realize that when a sensor can alter the FI system, a human can also do that, and hence Closed Loop FI systems are the preferred ones for the bikes which have multiple fuel mapping/drive modes in them. So Which One Is Better?
This is a very good question actually as to which one is better. Both have their advantages and disadvantages. While the open loop system is a very simple no nonsense types, the closed loop system is a lot accurate and can adapt easily to any kinds of atmospheric conditions. So if you are looking for the best thing to go about it, Closed Loop is always better since it was the one who arrived after the open loop system and is the newer tech among the two.
READ ALSO: Motorcycle Fuel Management System (FMS) Explained
One has to remember that if the oxygen sensor from the closed loop system is removed, it will operate like an open loop system, so to make it work like a closed loop system; one has to make sure the O2 sensor is working properly and the ECU needs to be modified accordingly.
So when you go on to buy your next big bike or already have a bike with FI system in it, check it out as to which loop system it is running on so that you can change your riding style accordingly since in case of open loop FI system you just have to keep a constant throttle response, but in case of the closed loop system the throttle response has a huge impact on the FI system’s functioning and only with experience will you get to know the difference as to how it works.
By: Pratik Patole