Internal combustion engine

The invention relates to an improved internal combustion engine having an air cooled or liquid cooled cylinder head and a piston of low thermal conductivity and low thermal expansion material and a uniform clearance between the cylinder liner and piston around the circumference, the cylinder liner being provided with fins for cooling by natural convection in order to avoid loss of heat from the combustion chamber to the coolant for increased efficiency of the engine.

This invention relates to an improved internal combustion engine which may 
be of the air cooled type or the liquid cooled type. 
In air-cooled internal combustion engines, the cylinder head and the 
cylinder liner are provided with fins or such extended surfaces through 
which a blast of cooling air is forced by means of a fan or blower. In 
liquid-cooled internal combustion engines, the cylinder head and the 
cylinder liner are provided with jackets through which water or such 
liquid is forced by means of a pump. The cylinder head requires to be 
cooled to maintain the temperature of the valves, nozzles and lower part 
of the cylinder head below their permissible values. The cylinder liner 
requires to be cooled to maintain the temperature of the piston and the 
lubricating oil between the piston and the cylinder liner below their 
permissible values. The piston is commonly made of aluminium. If the 
temperature of an aluminium piston exceeds 300.degree. C., it tends to 
expand and seize in the liner. If the temperature of the lubricating oil 
exceeds 220.degree.-250.degree. C., it burns off to form resins and 
varnishes and causes ring sticking. Rarely, the piston is also made of 
iron alloy. Such piston can withstand temperature upto 
450.degree.-500.degree. C. without significant loss of strength. 
A disadvantage of such internal combustion engine is that part of the heat 
being produced in the combustion chamber is lost to the coolant with the 
result fuel consumption increases and efficiency of the engine decreases. 
A further disadvantage of such internal combustion engine is that there are 
chances of the lubricating oil getting overcooled with the result the 
piston friction increases and consequently fuel consumption increases and 
efficiency of the engine decreases. 
A still further disadvantage of such internal combustion engine is that in 
the case of compression ignition internal combustion engine low grade or 
low cetane fuels such as light diesel oil, crude oil or furnace oil can 
not be burnt efficiently because of their high viscosity. 
Another disadvantage of such internal combustion engine is that clearance 
between the piston and the cylinder liner is comparatively more and varies 
along the piston pin axis and across the piston pin axis with the result 
lubricating oil between the cylinder liner and the piston is comparatively 
more and its thickness is uneven and it requires considerable coolant to 
get itself cooled. 
An object of the invention is to obviate the aforesaid disadvantages and 
provide an improved internal combustion engine wherein the cylinder liner 
is cooled by natural convection. 
A further object of the invention is to provide an improved internal 
combustion engine which burns low grade or low cetane fuels efficiently. 
A still further object of the invention is to provide an improved internal 
combustion engine wherein clearance between the cylinder liner and the 
piston is uniform around the circumference and is less than that of a 
conventional internal combustion engine of equivalent size and speed so 
that comparatively less coolant is required to cool the lubricating oil 
between the cylinder liner and the piston. 
Another object of the invention is to provide an improved internal 
combustion engine which consumes comparatively less fuel and is 
comparatively more efficient. 
The invention provides an improved internal combustion engine wherein the 
cylinder head is air cooled or liquid cooled and the piston is made of 
materials of low thermal conductivity and low thermal expansion such as 
cast iron or cast steel characterised in that the clearance between the 
cylinder liner and the piston is uniform around the circumference and is 
less than that of a conventional internal combustion engine of equivalent 
size and speed and the cylinder liner is provided with fins or such 
extended surfaces to cool the cylinder liner, the lubricating oil and the 
piston by natural convection. 
In the improved internal combustion engine, cooling by natural convection 
maintains the temperature of the lubricating oil below 
220.degree.-250.degree. C. and the temperature of the piston crown upto 
450.degree.-500.degree. C. The high temperature of the piston crown 
facilitates efficient combustion of the fuel and reduces specific fuel 
consumption of the engine. In the case of compression ignition internal 
combustion engine, the high temperature of the piston crown reduces delay 
period and ensures that the rate of pressure rise is comparatively less so 
as to render the engine smooth and vibration free. 
The fins may be perpendicular to or parallel to the cylinder liner axis. 
The cylinder liner may be made of aluminium, cast iron or cast steel. 
According to an embodiment, wherein the internal combustion engine is of 
liquid cooled compression ignition type circulation means may be provided 
for circulating low grade or low cetane fuels through the cooling jacket 
of the cylinder head prior to feeding the said fuel to the fuel injection 
pump and thence to the fuel injection nozzle. 
Preferably, the circulation means may comprise a flow pipe connecting the 
fuel tank of the said engine and coolant inlet of the said jacket, one or 
more fuel filters provided with the flow pipe and a return pipe connecting 
the coolant outlet of the said jacket to the said fuel tank and also to 
the fuel injection pump of the said engine.

In FIGS. 1 and 2 like reference numerals indicate identical parts. 
Referring to FIG. 1, the internal combustion engine is a liquid-cooled type 
and consists of a liquid-cooled cylinder head 2 having a coolant inlet 4 
and a coolant outlet 6 and a fuel injection nozzle 8 connected to a 
fuel-injection pump 10 via a high pressure pipe 12. The engine also has a 
piston 14 made of cast iron or cast steel adapted to operatively move in a 
cylinder liner 16 which may be made of cast iron or cast steel or even 
aluminium. The crown of the piston is marked 18 and the piston ring zone 
is marked 20. The cylinder liner 16 is fitted with fins which cool the 
cylinder liner, lubricating oil and the piston by natural convection. The 
clearance between the cylinder liner and the piston is uniform around the 
circumference. The crank case assembly marked 22 is of any conventional 
construction. 
The cylinder head may be air cooled instead of being liquid cooled in which 
case a blast of air is forced through fins or such extended surfaces 
provided in the cylinder head by a fan or blower. In this case, the duct 
through which air is blown will be connected to the air inlet of the 
cylinder head. The air will flow in through the air inlet of the cylinder 
head and flow out through the air outlet of the cylinder head. 
FIG. 2 shows another embodiment which is identical to that shown in FIG. 1 
except that it has additionally a circulation means consisting of a flow 
pipe 26 (provided with fuel filters 28) connecting the fuel tank 24 of the 
said engine to the coolant inlet 4 and a return pipe 30 connecting the 
coolant outlet 6 to the fuel tank 24 and also to the fuel injection pump 
10. From the fuel tank, part of the fuel which is a low grade or low 
cetane fuel, enters the cylinder head through the flow pipe and the 
coolant inlet and goes to the fuel injection pump through the coolant 
outlet and the return pipe after taking away heat of the cylinder head 
along with it. As can be seen, part of the fuel from the fuel tank enters 
the fuel injection pump through the return pipe directly. Fuel that is 
coming from the cylinder head and that is coming from the fuel tank 
directly gets mixed up. Temperature of the mixed up fuel being higher than 
that of the fuel in the fuel tank its viscosity is less and it flows 
faster. 
The following is a comparative study of the conventional internal 
combustion engine and the improved internal combustion engine: 
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Conventional internal 
Improved internal 
combustion engine combustion engine 
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1. the cylinder liner and 
1. the cylinder liner and the 
the piston and the lubricating 
piston and the lubricating 
oil between the cylinder 
oil between the cylinder 
liner and the piston are 
liner and the piston are 
cooled by circulating liquid 
cooled by natural 
through a jacket provided 
convection. 
on the cylinder liner or by 
blowing air through fins or 
such extended surfaces 
provided on the cylinder 
liner by a fan or blower. 
2. since the clearance between 
2. since the clearance between 
the cylinder liner and the 
the cylinder liner and the 
piston varies along the piston 
piston is uniform around 
pin axis and across the piston 
the circumference and is 
axis and is comparatively 
comparatively less 
more lubricating oil in the 
lubricating oil required is 
clearance is comparatively 
less and cooling 
more, its thickness is uneven 
required is less. 
and it requires more coolant 
to get itself cooled. 
3. since the clearance between 
3. since the clearance between 
the cylinder liner and the 
the cylinder liner and the 
piston is comparatively more 
piston is comparatively 
leakage of blowby gas past 
less, leakage of blowby 
the piston and piston rings 
gas past the piston and 
into the crank case is piston rings into the crank 
comparatively more. case is comparatively less. 
4. the fuel is not being used as a 
4. the fuel can be used as a 
coolant to cool the coolant to cool the 
cylinder head. cylinder head in which 
case no additional 
coolants such as water or 
air would be required to 
cool the cylinder head. 
5. low grade or low cetane 
5. low grade or low 
fuel cannot be burnt cetane fuel can be burnt 
efficiently. efficiently. 
6. the fuel consumption is 
6. the fuel consumption is 
comparatively more. comparatively less. 
7. comparatively less efficient. 
7. comparatively more 
efficient. 
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In this specification, wherever the word `comparatively` is used it is to 
be understood that comparison is between an improved internal combustion 
engine of a particular size and speed and a conventional internal 
combustion engine of equivalent size and speed.