Monday, March 21, 2011




The increasing industrialization and motorization of the world has led to a steep rise in the demand for petroleum products.Petoleum products have given rise to many problems in automobile environment, because they give pollution and also they are under great demand. We used the THROTTLE BODY INJECTION SYSTEM, which plays significant role in reducing the emission level. We developed the TBI system which replaces the conventional carburetor system in the two wheeler four stroke gasoline engine by the use fuel injection pump fuel injector. Better fuel economy and less fuel consumption would be obtained and then the emission is less. Already throttle body, MPFI systems are only succeeded in four wheelers. But here we have try to implement in case of two wheelers.

We took a 350-cc single cylinder four stoke bullet gasoline engine as a test engine and the nozzle is mounted on the cylinder head intake manifold to get the throttle body fuel injection and the drive is taken from the timing gear wheel to drive the fuel injection pump. The results obtained from the test engine indicate that the engine was run successfully with gasoline by using throttle body fuel injection and also the emission levels were drastically reduced. When we are comparing base engine and modified engine the BHP is increases above 3.2 %. Torque is above 3.75% .and emission is reduced above 50%


Sweeping challenges have taken place in the automotive industry over the years that have led to engineering and design improvements in the field of fuel economy and pollution control and better fuel economy. One of the techniques is fuel injection.

Fuel injection in gasoline engine is less critical than that for diesel engine because the injection pressure is very much lower &timing is less sensitive. Since the fuel is not directly into the compressed air in the engine with a gasoline engine as it is with a diesel engine, the spray of gasoline has less penetration, but it still require good atomization characteristics. This repot explains the conventional carburetor engine drawbacks in case of two wheeler, injection system, and fabrication details of our project and test results. Finally we compare the performance of the base engine and our modified engine.


Ø In case of two wheeler, to modify the conventional carburetor system into throttle body injection system.

Ø To get higher horsepower and cleaner exhaust compared to the base engine.

Ø To reduce the specific fuel consumption of the engine.

Ø Increasing the engine life.


Conventional two wheeler carburetion system has lot of draw backs so it leads to invention of petrol injection system. Before seeing the injection system we should know the definition and disadvantages of carburetion system.


In SI engine a combustible fuel-air mixture is prepared outside the engine cylinder. The process of preparing this mixture is called carburetion and the device which does this is called a carburetor.


v Carburetor acts as a first link to control engine breathing.

v When we are going to carburetor system, the volumetric efficiency will drastically reduced because actual air intake is less than theoretical intake charge due to the presence flow restrictions in venture and bents in manifold flow passage.

v Heating of the incoming charge by a hot intake port in proximity to the intake manifold, causing the air-fuel mixture to expand before entering the cylinder.

v The mixture must be rich to ensure that the cylinder located farthest away from the carburetor get enough fuel. This cause the engine to run over rich. This is the big handicap for both fuel economy and emission control.

So we are in condition to go for gasoline injection in the manifold.


· Carburetor has more wearing parts .After wear it operates at less efficiency.

· Freezing may take place at low temperature unless special means are provided to obviate this problem.

· Back firing may take place and there is a risk fuel ignition outside the carburetor.

· Carburetor can act well only at particular speed and load.

· The coefficient of discharge of fuel and air will vary with respect to venturi depression. Whereas the coefficient of discharge for air becomes almost constant at certain value of depression, the coefficient for fuel increases gradually. This mans that at higher at higher speeds; the air fuel goes on becoming rich and richer. The fore the best fuel economy cannot be maintained.



A single point fuel injection system is also called throttle body injection system. It has the injector nozzle in the throttle body assembly on the top of the engine. Fuel is sprayed in to the top of intake manifold single point (one location).


A multipoint injection system is also called port injection system has a fuel injector in the port to each cylinder. Fuel is sprayed in to each intake valve, hence a term multi-point fuel injection system.


Comparing with carburetor method, an important drawback of using carburetor for metering fuel supply of multi cylinder engine is that it becomes difficult for a single carburetor to ensure uniformity of mixture quality in all the cylinders. Thus some may be getting weaker, while the others may be supplied with the mixture richer than desired. Further the throat of the carburetor causes a restriction in the air flow passage, and if the throat is made larger, if the problem of suitable mixture supply becomes acute at low speed as with the larger throat, the air velocity decreases which causes less efficient atomization and also fall in mixture strength. To obviate this above problems, multiple carburetors show the solution of all these troubles has found in the use of petrol injection. In this the petrol in the atomized form is sprayed into the air stream. Because in this system the petrol is already atomized, the mixing with the air stream is much better, giving a homogeneous air-fuel mixture, which burns more efficiency in the engine.

Mechanical Fuel Injection Control:

This type of control uses the throttle linkage, a mechanical pump and a governor speed device to control the injection quantity. This is a very old system used for high performance of racing cars. We adopted this type for our project work.


In this an injector assembly is attached to a throttle body. This Injector-throttle body assembly is installed on the intake manifold in place of a carburetor. This method simplifies the construction of the engine block and also does not obstruct hot-spots near the valves affecting the cooling water jacket size at that place. Moreover, it requires only one circuit in the computer to control injection. However, the later is more precise since in that case the fuel delivery does not depend upon air to carry the fuel through the intake manifold. Nevertheless the throttle body injection controls the fuel better than carburetors. We adopted this system for our project work.


AVL’s development of a semi-direct injected two stroke engine is placed on the investigation of fuel jet and scavenges flow interaction. To evaluate the scavenge flow pattern, a steady flow test procedure was developed and applied. The results of scavenging systems optimization were confirmed by subsequent engine tests which showed significant gains in power output.

Completion of the first phase of the research program resulted in pressure manifold injection system components. Compared to the original carburetor engine significant improvements were demonstrated, including a 30% reduction of fuel consumption, a reduction of up to 60% in hydrocarbon emissions and up to 70% in carbon monoxide emission, averaged over the engine’s speed and load range. Engine b.m.e.p and power characteristics were maintained and improved. In addition the critical idle operating conditions were improved significantly by stabilizing the combustion which minimized cyclic variations.

advantages of fuel injection SYSTEM:

Ø Much better cylinder fuel injection therefore more even load distribution between cylinders. With less tendency towards detonation because of lean air/fuel mixture ratio.

Ø An average of 10% increase in engine power due to better volumetric efficiency which is achieved with the use of larger air inlet passages. This is further assisted by cooler fuel that is delivered directly by the fuel vaporization. Increased valve overlap is generally possible as well as the elimination of air throttling and heat transfer imparted to the incoming air.

Ø Leaner air/fuel ratio can be more easily obtained along with provision for fuel shut off during coasting or declaration such as is now available on some imported vehicle.

Ø Faster acceleration is usually available because atomized fuel is delivered directly to the inlet valve port with port type fuel injection for momentary fuel enrichment.

Ø A wide range of fuel can be employed because of mechanical atomization of the fuel.

Ø In aircraft application, carburetor icing is minimized, because the gasoline is vaporized at the inlet valve or port in the engine cylinder.

Ø Reduction or elimination of back firing in the inlet manifold or throttle body.

Ø Higher engine torque, quicker start and engine warming.

Ø Closer control of air/fuel mixture and the ability to maintain Stoichiometric conditions overall operating conditions.

Ø Less exhaust emission because of the ability to maintain stoichiometric conditions.

Ø Elimination of many pollution control devices required with carburetor system.

Ø No requirement for mixture screw adjustments as with carburetor system.

Ø Better fuel economy.

Ø No choke system required.

Mechanical fuel injection control

In the mechanical injection type the fuel from the fuel tank to the pump is taken by using a delivery tube (two wheelers) or by feed pump (four wheelers). The pump is driven by an eccentric (or) can which is in the timing gear, cam shaft or crank shaft. The main function of fuel injection pump is to deliver accurate amount of fuel in to the engine cylinder for combustion in certain pressure. Generally employed in case of automotive petrol engine fuel injection range from 284 k Pascal to 325 K Pascal. There is a sleeve which is control by the driver through accelerator petal for varying the speed. The pump pumps the fuel into the injector and due to the pressure atomization takes place. The injector is otherwise called nozzle, atomizer or fuel valve. Its function is to inject the fuel into the cylinder in proper quantity.


engine modification:

In our experimental engine we removed the carburetor and fitted with Fuel injection system i.e. the pump and the nozzle.

Fuel Pump Set Up:

In order to achieve the delivery of fuel once every cycle the drive for driving the fuel injection pump is taken from timing gear wheel shaft. By removing the existing cover of the timing gear wheel shaft and fitted with new designed cover in order to place the pump. For pump operation a cam is fitted in the timing gear wheel shaft and tappet is also provided for lifting.

Nozzle Set Up:

The injector is placed at intake manifold for injecting the petrol. Low-pressure injector is sufficient for inject petrol. So in our project, we used the low pressure modified multi-hole nozzle. The injector is placed tightly with the intake manifold by using flange arrangement.


The modified experimental engine and eddy current dynamometer was coupled by chain drive. The chain was connected to the engine pinion to rear sprocket fitted on the frame. The engine ignition key was connected to the dynamometer control panel for engine over speed setting and tripping. Fuel line from fuel tank was connected to the inlet of the injection pump through burette. Electric supply and cooling water supply was given to the dynamometer. Battery supply was given to the engine for ignition purpose. Engine cooling arrangements were set. Figure shows the experimental set up for manifold injected spark ignition engine.


1. The electric power is switched on and the engine is allowed to warm for some time.

2. Initially the potentiometer is kept at zero position.

3. The dynamometer is loaded and damping switch is adjusted to get the stable reading.

The Benz system load control mode switch ‘M’ is switched on for taking Reading. The load controller also takes cares the safety factor of the eddy current dynamometer like dynamometer water pressure, dynamometer case Temperature etc. Engine over speed setting and tripping of the engine is set on control Panel.

load and speed measurement

For getting the rated dynamometer speed (460,520,660,720) the load was given on the engine. The engine speed was calculated from the dynamometer speed. A sensor measured the load given by the dynamometer and it was indicated on the control panel.

fuel consumption measurement

Fuel consumption of the engine was measured by using the conventional burette and stop Watch arrangement. The time requires for 50 cc consumption was measured at every throttle condition.

hydrocarbon and carbon-monoxide measurement

The unburned hydrocarbon and carbon-monoxide measurement were made with HORIBA INFRARED ANALYSER. The readings were taken at each operating conditions.


After completing all the modifications such as mounting the fuel injection pump, mounting the injection nozzle, etc were made in the base engine, first we fixed the injection time at which the fuel injected is fully mixed with air. Then the injection opening is kept at a pressure of 150kg/cm2. For this opening pressure, the engine performance was taken. Then by comparing the performance of the engine, the pressure at which the engine gives more power was determined and the corresponding injection pressure 140kg/cm2 was fixed after fixing the injection pressure, the injection timing was set.


We have comparing the base engine with the modified engine at 1/2throttle position and the following results were obtained. The reason for choosing 1/2throttle condition is that the fuel economy will be better.

Finally we concluded that throttle body injection system for two wheeler four stroke S.I engine is most appropriate.

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