Introduction to MPFI

INTRODUCTION:

•  MPFI stands for MULTI POINT FUEL INJECTION. 
• It is an improvement over carburetors. It allows more efficient combustion of fuel, thereby producing more power with lesser emissions. 
• It is a technology similar to what CRDI is in diesel engines.

NEED FOR MPFI:

•  In carburetor, air and fuel are mixed in a fixed ratio and sent to the cylinders for combustion. 
• This is a purely mechanical system with negligible flexibility.
•  It often sends more fuel into the cylinder than the available air, thereby leading to incomplete combustion, high fuel consumption and excess emissions. 
• This also leads to carbon deposits inside the combustion chamber and reduces engine life.

BASIC CONCEPT:

•  MPFI is an intelligent way of doing what a carburetor does.
•  In this system each cylinder has injectors to spray the fuel/air charge into the cylinders. 
• The fuel and air are mixed in what is called the intake manifold. 
• In MPFI, each injector in controlled by the ECU.
•  The ECU monitors various engine parameters and accordingly decides just how much fuel is to be injected into the cylinder and at precisely what time .
•  This system also allows each cylinder to be controlled independently.

TYPES OF MPFI SYSTEMS:

 The various types of MPFI systems are: 

1. Simuntaneous : Together in all the cylinders. 

2. Sequential : Direct injection into the individual cylinders against their power strokes.

 3. Group : In cylinder pairs [in V engines]

TYPES OF MPFI SYSTEMS:

 Choosing the correct technique according to the engine configuration results in: - better power balance between cylinders - higher output from each cylinder - faster throttle response Of these technologies, sequential gives the best combination of power balance and output in inline 4 cylinder engines.

ADVANTAGES OF MPFI:

 (1) More uniform A/F mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum.

 (2)Vibration from the engine equipped with this system is less, due to this the life of engine components is improved. 

(3) No need to crank the engine twice or thrice in case of cold starting as happens in the carburettor system. (4) Immediate response, in case of sudden acceleration / deceleration. 

(5) Since the engine is controlled by ECU, more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level. 

(6) The mileage of the vehicle will be improved.

INJECTORS:

•  These are precision built solenoid valves. 
• They have single or multiple orifices which spray fuel into the intake manifold. 
• The fuel is taken from a common rail/header, pressurized to around 3 bar, fed by a high pressure fuel pump.

INJECTOR CARE:

INJECTOR CARE Fuel injectors can get clogged by olefin wax, water, dirt and other debris material present in the fuel or in the intake manifold. As such they require some basic maintenance and periodic cleaning. - Regular service of vehicle at specified intervals - Use of unadulterated and recommended grade fuel - Use of specialized injector cleaner additives - Periodic cleaning of injectors on injector cleaning machine.

ECU:

ECU ECU or the Electronic Control Unit is the brain behind the MPFI system. It is a computer chip which receives input on various engine parameters, compares them against preloaded engine and throttle maps and accordingly decides exactly how much fuel is to be injected into which cylinder and at what time

ECU:

ECU Because of this, the engine becomes more cleaner, more responsive and uses lesser fuel. Modern ECUs have memory by which they can learn the user’s driving style. For e.g., if someone has a habit of speedy pick up, the ECU will remember that and give more power at lower rpm by injecting in more fuel. It will judge by the amount of pressure being put of the throttle.

 The various parameters monitored by the ECU are: 

Ambient temperature 

Coolant temperature 

Exhaust temperature 

Exhaust Oxyzen content 

Inlet manifold vacuum 

Throttle position

 Engine rpm 

Vehicle road speed 

Crankshaft position 

Camshaft position

 Outside air pressure 

Pressure on throttle

ECU CHIPPING:

•  Manufactures program the ECU for general use keeping in mind fuel efficiency, engine life, service intervals fuel quality and diverse usage conditions. 
• The engines are made to develop only a fraction of the output which they actually can produce. ECU Chipping refers to modifying the original ECU programming to alter the way it reacts to certain inputs, in order to maximize engine performance

 This is done to change engine power and torque, performance characteristics at a particular rpm, engine rpm limit, road speed limit, engine timing etc. Chipping can be done either by overriding the original ECU with a specially designed one or by simply remapping the original ECU as per requirement.

 By chipping the ECU, we can significantly increase the engine’s power and torque and rpm limit for drag races etc. 

We can change the mapping to improve pick up in a particular rpm range, like for reducing turbo lag. We can get custom maps developed for our own driving style. 

Commercial vehicles can be fitted with speed limiters and be mapped for torque and reduced rpm in interest of safety and to boost engine life and economy.