The present invention relates to a two stoke internal combustion engine with provision for enhanced cooling.

Internal combustion engines are used as prime movers in many vehicles. These engines produce significant amounts of heat during the course of their operation. A part of the heat energy generated inside the combustion chamber is dissipated to the atmosphere. The dissipation of heat from the engine at higher rate is desirable to keep the engine temperature within the desirable limit. To achieve proper cooling, engines are fitted with various cooling systems. These cooling systems rely on a flow of fluid over or through the engine casing or engine components as a means of transferring heat from the engine to the environment. Inefficient engine performance and failure of engine components have been observed due to failure of heat transfer from the engine.

Air is generally used as an agent for transferring heat from the engine to the ambient and such engines are often referred to as being "air-cooled" engines. A typical air cooled engine consists of at least one cylinder structure encasing at least one reciprocating piston and a cylinder head. The cylinder head is mounted atop the cylinder block and provides a combustion chamber as well as for housing intake and exhaust valve or port mechanism depending upon the engine type.

Irrespective of the engine types and irrespective of how many cylinders or how each cylinder is physically oriented with respect to another cylinder, the engine is usually positioned to permit a flow of air over and about the engine. To enhance the rate of heat transfer to the ambient air generated by the combustion of fuel and air within the engine, or more precisely the heat generated within the cylinder block and the cylinder head where such combustion takes place, the engine is often fitted with a number of cooling fins which extends outwardly from the from the engine. It is widely recognized within the art of constructing engines which employ cooling fins, that cooling fins serve to increase the effective surface areas from which heat is transferred to the environment generated from within the engine and its associated components. With increase in effective surface area provided by the cooling fins, the rate of radiative and convective heat transfer to the environment is increased. Number, size, orientation, design and position of fins on the engine further influence cooling capacity of such fins.

The present invention provides an engine cooling system that would facilitates heat transfer due to natural air and forced air-cooling simultaneously for engine liner temperature reduction. The fins on the cylinder block are made vertical so as to facilitate passage ambient air coming from the cylinder head. This makes the cylinder head and block fins parallel to each other. To facilitate the cooling from the fan, groves from both sides in the fins near the exhaust port are provided. These groves would act as a passage for air both from the fan and ambient air coming from the cylinder head. The forced air from the fan would cool the exhaust port fins near it. The heat transfer from the other side of the groove would happen from the ambient air. Since cooling air passes close the engine liner, temperature reduction is expected in the liner.

Temperature measurement shows reduction of temperature in the cylinder block when grooves are used. Following table summarizes the benefits in temperature reduction. Temperature drop of about 5 deg. Celsius was observed both in liner and exhaust port. These data are for a typical two-stroke small displacement engine and temperature drop would vary from design to design and engine capacity. However, this invention illustrates that providing provision for both natural and forced cooling would help in engine temperature reduction.

Table 1. Temperature comparison with and without grooves in the cylinder block.
Block liner Exhaust port
temperature (°C) temperature (°C)
Block with grooves 222 195
Block without grooves 227 200

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter.

The two stroke internal combustion engine with provision for enhanced cooling, according to this invention, comprises a cylinder head and cylinder block wherein the fins on the cylinder block are parallel to the fins on the cylinder head; first and second sets of reliefs provided at the exhaust port from both sides whereby natural air and air from the cooling fan pass through the said sets of reliefs such that at higher vehicle speeds air coming from the cylinder head forces the air from the fan towards engine crankcase side and at lower vehicle speeds or in standstill condition, air from the fan cools both cylinder head and block.

This invention illustrates in

Figure 1 . Vehicle with horizontal engine.

Figure 2. Prior art engine cooling system in horizontal engine, (a) top view and (b) front view

Figure 3 Engine cylinder block with grooves, (a) top view (b) side view

Figure 2(a) shows the engine cooling system with forced-air cooling. Forced air from the centrifugal fan is guided by cowl 5 and directed to the engine block specifically to engine exhaust port 3. The cylinder block is mounted on engine crankcase 6. Fins of the cylinder block 2 are aligned to the flow coming from the fan. However, these fins are perpendicular to the fins on the cylinder head (figure 2b). The design of the cylinder head is suitable for natural air coming from the front where as the design of the cylinder block fins are suitable for the air coming from the fan. The flow of air in the block from the fan is perpendicular to the flow in the cylinder head. Hence, the natural cooling air entering the cylinder head cannot be utilized properly for cooling the block. And the air coming from the fan to the block cannot be utilized for cooling the cylinder head. Hence, the cooling system design requires that in the event of fan not working, the natural air can still cool the engine.

Figure 3 shows one aspect of the invention depicting the design of cylinder block. Fins on the cylinder block are made parallel to the fins on the cylinder head. This ensures that air coming the cylinder head also cools the cylinder block fins and its components. However, cylinder block fins are now perpendicular the flow coming from the fan. To overcome this problem, reliefs (7, 8) on the exhaust port is provided from both sides (figure 3a). Air from the fan passes though the relive 8 while the natural air passes through the relieve 7. Air from the fan enters the relieve 8 and goes either towards the cylinder block or towards the crankcase depending upon the engine speed. At higher vehicle speed, air coming from the cylinder head forces the air from the fan towards engine crankcase side. At lower vehicle speed or in standstill condition, air from the fan cools both cylinder head and block. The air from the relief 8 cools block first, goes upward and cools the cylinder head. Hence, this invention works in both the conditions when either the vehicle is moving or at standstill. As discussed in table 1, reduction in the engine cylinder block liner temperature was observed when the reliefs were provided at the exhaust port.

It will be appreciated that various other embodiments of this invention are possible without departing from the scope and ambit thereof.

We Claim:

1. A two stroke internal combustion engine with provision for enhanced cooling comprising a cylinder head and cylinder block wherein the fins on the cylinder block are parallel to the fins on the cylinder head; first and second sets of reliefs provided at the exhaust port from both sides whereby natural air and air from the cooling fan pass through the said sets of reliefs such that at higher vehicle speeds air coming from the cylinder head forces the air from the fan towards engine crankcase side and at lower vehicle speeds or in standstill condition, air from the fan cools both cylinder head and block.

2. A two stroke internal combustion engine substantially as herein described with reference to, and as illustrated in, the accompanying drawings.