Electronic Multipoint Fuel Injection System

Electronic Multipoint Fuel Injection System

INTRODUCTION Now a day, the digital revolution is taking place increasingly and dominating the 1990's. Or rather we can call the 1990's as the digital decade. Because much more and more advancement is taking place in the field of electronics engineering only on the basis of a word digital.

Many examples can be quoted. LP's have been replaced by the digitally recorded compact discs usually called as CD's. Personal computers which works on a digital processing are becoming an essential home appliance every where in many of the home appliances digital control units sire provided for easy control of parameters and for convenience of users.

The word digital has a meaning behind it that to reduce any process or input to the basic, extremely precise numerical components. The word digital had taken a place of analogue, which is a very complicated procedure, while digital is simplified one.

Due to the simplified operation of digital processors it had introduced many techniques, which dominates the variety of industries & which are resulting beneficial to the industries. In the field of music industry the digital CD's were introduced giving finest quality of output. The recently introduced term i.e. 'surround sound' is based on the digital processing which is again increasing the quality.

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Electronic Multipoint Fuel Injection System

Now the point of attention is that one digital element that touches all of our lives daily is, in our automobiles. Near about all the automobiles are taking the benefits of word digital. We can say every car running on the road has at least one digital element in it. The word digital had penetrated or reached the heart of an automotive i.e. the engine. The carburetors, which are now absolute, are being called the 'dinosaurs' of the automobile engineering and the digitally controlled fuel ignition system had been introduced in the engines of automotive.

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Electronic Multipoint Fuel Injection System

NEED OF FUEL INJECTORS About a decade before, the mean of supply of the fuel to the engine was the device, called carburetor. As the evolution in the automotive took place, the carburetor became more and more complicated in structure. Since it had to handle many of the operations. For serving the purpose five circuits were provided in it for performing different operations. For obtaining the stricter emission requirements catalytic converters were introduced. And for its effective working the very accurate control over the air-fuel ratio must be there. The carburetor had failed to monitor the exact amount of oxygen in the exhaust and thereby maintaining the correct air-fuel ratio for it. There were electrically controlled carburetors for long time but still they were much more complicated than the pure mechanical one. These drawbacks gave the birth to fuel injectors.

In the beginning the throttle body fuel injection system were introduced. Which is also called single point or central fuel injection system. Gradually as new engines were produced this system was replaced by the Multipoint or multiport fuel injection systems. Which are operated electronically using performance chips.

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Electronic Multipoint Fuel Injection System

TYPES OF INJECTION SYSTEMS 1) Throttle body injection (TBI): It is usually called as single port injector, placed before the throttle plate. K looks more or less like a carburetor. In this system one injector feeds all the cylinders. Some times two injectors may be used side by side. In these cases, what happens, two injectors are placed above the throttle blades in the air valve. The fuel sprayed by the injectors hits directly the blades of throttle valve and sticks there. That's why the uniform distribution of the fuel in the air stream does not take place. This uneven distribution ultimately lowers the efficiency, performance and produces low power.

TBI systems usually runs at low pressure fuel systems i.e. 15 psi.

2)

Multipoint fuel injection (MPFI): It means the number of injectors is more than two i.e. one injector for

each cylinder for ex, 6-cylinder = 6 injectors.

Here the injector is situated at the intake plenum and pointed towards the intake valve of a cylinder. There are two firing circuits provided in this system. Working pressure of fuel is about 45 psi. For the purpose of extra fuel during cold start, an additional injector is oftenly provided.

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Electronic Multipoint Fuel Injection System

3)

electronics multi point fuel injection (EMPFI) : Here the word electronic stands for the electronical operation of the

injectors valves. Here the opening and closing of each injector valve is directly controlled by the electronical circuits provided.

4)

Sequential Fuel Injection (SFI) : It's a type of multi port or multipoint fuel injection system. Here each

cylinder has one injector which is provided by individual firing circuit.

In this system each injector opens just before the intake valve of a cylinder opens. The advantage of SFI is that, it responds more quickly to the sudden change made by driver because from the time the change is made, the valve only has to wait until the next intake valve opens instead of for the next complete revolution of the engine. It results in better emissions and probably gives more power. It runs at the same pressure as the MPFI runs.

5)

Tuned port injection (TPI) : It is same as the MPFI only the difference is that it has more number

of cylinder. Ail the MPFI and TPI injectors are physically interchangeable. Only they have different fuel flow rates.

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Electronic Multipoint Fuel Injection System

CONSTITUENTS OF EMPFI SYSTEM This system includes the following major parts :

1] Sensors: Sensors are the sensing elements located at different places for collecting the necessary information about current working condition of the engine. They sense the different parameters like pressure temperature speed air flow rate etc. Sensors send this information to the ECU.

2] ECU : Engine control unit (ECU) uses the information collected by sensors and make calculations and send the result towards the actuators.

3] Performance chips : They are situated in the ECU and are the data storing elements and may be called as a minicomputer in the fuel injection system.

4] Injector valves : These are the actuators basically. They receives signal from ECU and does function accordingly.

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Electronic Multipoint Fuel Injection System

EMFI-HOW IT WORKS ? Here, there in starting from a gas pedal which is pushed to accelerate the vehicle. It is connected directly to the throttle valve which has a function of supplying oxygen rather air into the engine. So the gas pedal is actually the air pedal regulating the amount of air being supplied to the engine. As soon as the pedal is pressed the throttle valve opens up more, letting more amount of air in the cylinder. Now to balance the stoichiometric ratio there must be increase in the amount of fuel entering the engine through injector. Otherwise some air may enter without sufficient fuel with it which will change the stoichiometric (air-fuel) ratio and may result in lowering the efficiency. Hence an ECU, which controls all the electronic components in the systems, is connected to the injector valve. It takes information from the oxygen sensors. These oxygen sensors are connected to the air valve and ECU. It decides the amount of oxygen in the engine and exhaust and sends this information to ECU. ECU, after collecting the information opens the injector valve in specific proportion. So that stoichiometric ratio is just maintained. These fuel injectors are nothing but the electronically controlled valves. Whose opening time depends upon ECU. The valves are supplied with pressurised fuel by means of fuel pump present in the vehicle. This valve is cable of opening and closing many times in a second. Inside fuel injector when injector is energized, a plunger which is operated by electromagnet, opens the valve. Which allows the fuel under pressure to squirt out through a tiny nozzle. This nozzle is designed to atomise the fuel in fine spray or mist as possible so that its combustion will be easy.

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Electronic Multipoint Fuel Injection System

ECU & PERFORMANCE CHIPS ECU controls the amount of fuel entering the engine by having the control over the opening and closing of injector valve. There are two main types of the control for multipoint injection systems. 1)

All the fuel injectors can open at the same time.

2)

Each one opens just before the opening of intake valve of its cylinder (called

sequential fuel injection). The amount of fuel entering the engine depends upon the time for which the valve remains open and this time is called the ' pulse width'. So ECU decides the pulse width actually. ECU calculates this pulse width which varies according to the operating conditions of the engine. For finding some factors involving in the calculation, ECU uses the information obtained by the different sensors located in the circuit. Some of them are listed below :

1. Mass airflow sensor : - tells the ECU, the mass of air entering the engine.

2. Oxygen sensors : - controls the amounts of oxygen in the exhaust so that the ECU can determine how rich the fuel mixture should be and accordingly makes the adjustment.

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Electronic Multipoint Fuel Injection System

3. Throttle Position Sensor : -monitors the position of throttle valve (which senses how much air into the engine) so that the ECU can respond quickly to changes, varying the fuel flow rate.

4. Coolant temperature sensor : -allows the ECU to determine when the engine has reached the proper operating temperature.

5. Voltage sensor : -monitors the system voltage in the car so the ECU can raise the idle speed if the voltage is dropping (Which indicates the high electrical load).

6. Manifold absolute pressure sensor : - monitors the pressure of the air in the intake manifold. The amount of air being drawn into the engine is a good indication of how much power it is producing as more air entering the engine, lowering the manifold pressure, so this reading is used to gauge how much power is being produced.

7. Engine speed sensors : - senses the engine speed which is one of the factor in calculating the pulse width.

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Electronic Multipoint Fuel Injection System

ECU uses the formula for calculation of a pulse width i.e. required pulse width = Base pulse width (rpm, Load) × factor A × factor B × --- and so on.

For this calculation the base pulse width is found out by ECU which is a faction of engine speed in rpm and load which is calculated from the manifold absolute pressure recorded by the respective sensors. For finding the base pulse width and all the factors in the formula there are look up tables from which the corresponding values are chosen for the given operating conditions sad the required pulse width is calculated. These calculations are done by the performance chips and all the data such as number of look up tables are Stored in the same chips we can have an example.

In this example, for simplicity our equation will have only three parameters i.e. Pulse width = (Base pulse width (RJPM, Load)) × (Factor A) × (Factor B) Let's say the engine speed is 2000 rpm and the load is 4. So the number on the intersection of 2000 & 4 is 8 milliseconds as below :

RPM / Load 1000 2000 3000 4000

1 1 2 3 4

2 2 4 6 8

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3 3 6 9 12

4 4 8 12 16

5 5 10 15 20

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Electronic Multipoint Fuel Injection System

Now A & Bare the parameters came from sensors. Let's say A is coolant temperature and B is oxygen level. If A is 100 and B is 3, the following look up tables tells us the factor A == 0.8 and factor B = 1.0. A 0 25 50 75 100

Factor A 1.2 1.1 1.0 0.9 0.8

B 0 1 2 3 4

Factor B 1.0 1.0 1.0 1.0 0.75

So putting the obtained values in the formula we have the overall pulse width required. = 8 × 0.8 × 1.0 = 6.4 milliseconds From this example you will come to know that how the control system makes the adjustment. This is the calculation for one pulse width. And the injector valve has to open and close many times in a second. So for every different working condition of an engine, there is difference in pulse width ultimately the different calculations. In this way we can say a small computer in the form of ECU in which the brain called performance chips are situated works basically on the digital processing. It has to collect the information handle the data, calculate the result and finally is responsible for getting the proper amount of fuel inside the cylinder of an engine by having control over the pulse width of the injector valves.

MODES OF OPERATIONS OF EMPFI Government Polytechnic, Washim

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Electronic Multipoint Fuel Injection System

1] Open Loop Operation : During cold start or idle start the system works on the open loop operation. For this purpose the starter switch is also connected to the EMPFI system. As the key rotates over the shift lever the EMPFI system set over the open loop mode and started. In this mode of operation the oxygen sensors are ignored by the ECU. And the EMPFI controls to a fixed fuelling map.

Idle mixture adjustment : The electronic control unit (ECU) is just in the right side of the trunk and there is an opening in the side of ECU. In this opening there is I with one side flat. This shaft turns a little snaps and adjusts the baseline fuelling map during the idle which is responsible for the idle mixture.

2] Closed Loop Operation : When the engine is connected to any drive or any gear, the system started to operate on the closed loop mode of control. In this mode the system works normally as the specified air-fuel ratio and using all the sensors as discussed before.

ADVANTAGES OF EMPFI Government Polytechnic, Washim

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Electronic Multipoint Fuel Injection System

1) More uniform Air-Fuel mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this there is an improvement in the life of engine components.

2) No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system.

3) Gives immediate response, in case of sudden acceleration / deceleration.

4) Since the engine is controlled by ECM or ECU (Engine Control Module or Unit), more accurate amount of Air-Fuel 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.

5) The mileage of the vehicle will be improved.

CONCLUSION Government Polytechnic, Washim

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Electronic Multipoint Fuel Injection System

In above discussion we have understood that how the new fuel injection system works more efficiently than the previous carbs, how the performance chips gives us more power. After having discussion over this subject we are quite well known about the terms like injection of fuel, air-fuel ratio and its variation, and artificial intelligence of ECU.

This digital technology is an invention of 20th century and is apart of an artificial intelligence. This technology is developed in 20th century and will carry us in the 21st century along with its new forms.

May the new century give us more advanced and more comfortable technologies other than digital one.

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Electronic Multipoint Fuel Injection System

REFERENCES 1. I. C. Engine - by Mathur and Sharma

2.

www.googlesearch.com

3.

Automobile Engineering - by Kirpal Singh

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