24-08-2011, 02:40 PM
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HEMI ENGINE
INTRODUCTION
Engine is the basic component of any automobile.
Combustion engines may be divided into two general classes
Internal combustion engines.
External combustion engines.
Hemi engine is a four stroke , spark ignition, reciprocating type, internal combustion engines
BASIC DESIGN
The HEMI engine was first developed in1951 by the chrysler corporation.
The advantage of HEMI engine over other engines of the time was that it produced more power.
The reason for this was the efficiency of the combustion chamber.
BASIC FLAHEAD ENGINE DEAIGN
HEMI ENGINE DESIGN
In a HEMI engine, the top of the combustion chamber is hemispherical.
The combustion area in the head shaped like half of a sphere.
An engine like this is said to have “hemispherical heads”.
In a HEMI head, the spark plug is normally located at the top of the combustion chamber and the valves open on opposite side of the combustion chamber.
BASIC HEMI ENGINE DESIGN
MERITS AND DEMERITS
MERITS
There are many different pats of an engine design that control or determine the amount of power you can extract from each combustion stroke.
You want to burn all the gas in the cylinder. If the design leaves any of the gas unburned , that is untapped energy.
You want the maximum cylinder pressure to occur when the crankshaft is at the right angle so that you can extract all of the energy from the pressure.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as possible to the head and the cylinder walls.
Heat is one of the things creating pressure in the cylinder;
So lost heat means lower peak pressure.
All these factors are satisfied in the HEMI engine because of its design.
In a HEMI engine , surface area is much smaller than that in a flat head ,
And so less heat escapes and peak pressure can be higher
Another factor with a HEMI head is the size of the valves .
Since the valve are on the opposite sides of the head ,
There is more room for valve .
The engine design that preceded the HEMI was a wedge shaped combustion chamber with the valve in line with each other.
The in line arrangement with limmited valve size.
In the HEMI engine the valve can be large .
So that airflow through the engine is improvrd.
Thus the HEMI engine delivers more power owing to its design .
The design helps in attaining a higher degree of turbulence.
High volumetric efficiency, improved anti-knock characteristic and compactness of combustion chamber.
DEMERITS
Not all engines are using HEMI heads though they have the advantages mentioned .
This is mainly because of two reason.
One thing that a hemispherical head will never have is four valve per cylinder.
Another reason most high performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber
PENTROOF HEMI ENGINE DESIGN
RECENT DEVELOPMENTS
SUPERCHARGING
Supercharging is a method used to increase the density of air charge before it enters the cylinder. This allows more Oxygen for combustion than conventional methods. This results in better combustion and more power output.
CYLINDER DE-ACTIVATION
This engine featured cylinder de-activation using the multi-displacement system (MDS). The MDS turns off the fuel consumption in four cylinders when V-8 power is not needed. The system deactivates the valve lifters. This keeps the
valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders. This provides a world-class combination of power and fuel economy.
Specific Advantages
Generally, the engine appears to have been designed for lighter weight.
The new Hemi is precision cast, which allows it to be lighter than a typical 5.7 litre engine, even with a taller deck height than Chevy's; and, partly to counter the inertia of its relatively long stroke, the pistons were made light as well, using cast eutectic alloy
The skirt is coated to allow for variance in production piston sizes, increase the fit for ring seal, and reduce piston noise.
The lightweight wrist pin is also high-set
TWIN SPARK PLUGS
Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder
CONCLUSION
It is found that the power deliver by these engines Is greater then the power output from engine with i-head , h-head , l-head , t-head.
These engine are used in more and more in modern cars.
Though chrysler is the major user of this type of engines, other motor companies are also beginning to use these engines with some variations because of the patent protection that is present for these engines.
hemi engines also find in major application in car being used for racing purposes.
HEMI ENGINE
INTRODUCTION
Engine is the basic component of any automobile.
Combustion engines may be divided into two general classes
Internal combustion engines.
External combustion engines.
Hemi engine is a four stroke , spark ignition, reciprocating type, internal combustion engines
BASIC DESIGN
The HEMI engine was first developed in1951 by the chrysler corporation.
The advantage of HEMI engine over other engines of the time was that it produced more power.
The reason for this was the efficiency of the combustion chamber.
BASIC FLAHEAD ENGINE DEAIGN
HEMI ENGINE DESIGN
In a HEMI engine, the top of the combustion chamber is hemispherical.
The combustion area in the head shaped like half of a sphere.
An engine like this is said to have “hemispherical heads”.
In a HEMI head, the spark plug is normally located at the top of the combustion chamber and the valves open on opposite side of the combustion chamber.
BASIC HEMI ENGINE DESIGN
MERITS AND DEMERITS
MERITS
There are many different pats of an engine design that control or determine the amount of power you can extract from each combustion stroke.
You want to burn all the gas in the cylinder. If the design leaves any of the gas unburned , that is untapped energy.
You want the maximum cylinder pressure to occur when the crankshaft is at the right angle so that you can extract all of the energy from the pressure.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as possible to the head and the cylinder walls.
Heat is one of the things creating pressure in the cylinder;
So lost heat means lower peak pressure.
All these factors are satisfied in the HEMI engine because of its design.
In a HEMI engine , surface area is much smaller than that in a flat head ,
And so less heat escapes and peak pressure can be higher
Another factor with a HEMI head is the size of the valves .
Since the valve are on the opposite sides of the head ,
There is more room for valve .
The engine design that preceded the HEMI was a wedge shaped combustion chamber with the valve in line with each other.
The in line arrangement with limmited valve size.
In the HEMI engine the valve can be large .
So that airflow through the engine is improvrd.
Thus the HEMI engine delivers more power owing to its design .
The design helps in attaining a higher degree of turbulence.
High volumetric efficiency, improved anti-knock characteristic and compactness of combustion chamber.
DEMERITS
Not all engines are using HEMI heads though they have the advantages mentioned .
This is mainly because of two reason.
One thing that a hemispherical head will never have is four valve per cylinder.
Another reason most high performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber
PENTROOF HEMI ENGINE DESIGN
RECENT DEVELOPMENTS
SUPERCHARGING
Supercharging is a method used to increase the density of air charge before it enters the cylinder. This allows more Oxygen for combustion than conventional methods. This results in better combustion and more power output.
CYLINDER DE-ACTIVATION
This engine featured cylinder de-activation using the multi-displacement system (MDS). The MDS turns off the fuel consumption in four cylinders when V-8 power is not needed. The system deactivates the valve lifters. This keeps the
valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders. This provides a world-class combination of power and fuel economy.
Specific Advantages
Generally, the engine appears to have been designed for lighter weight.
The new Hemi is precision cast, which allows it to be lighter than a typical 5.7 litre engine, even with a taller deck height than Chevy's; and, partly to counter the inertia of its relatively long stroke, the pistons were made light as well, using cast eutectic alloy
The skirt is coated to allow for variance in production piston sizes, increase the fit for ring seal, and reduce piston noise.
The lightweight wrist pin is also high-set
TWIN SPARK PLUGS
Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder
CONCLUSION
It is found that the power deliver by these engines Is greater then the power output from engine with i-head , h-head , l-head , t-head.
These engine are used in more and more in modern cars.
Though chrysler is the major user of this type of engines, other motor companies are also beginning to use these engines with some variations because of the patent protection that is present for these engines.
hemi engines also find in major application in car being used for racing purposes.
