PROJECT TITLE AND TEAM MEMBERS

DESIGN AND ANALYSIS OF A TWO STROKE DESIGN AND ANALYSIS OF A TWO STROKE PETROL ENGINE TEST RIGPETROL ENGINE TEST RIG

INTRODUCTION A two stroke engine is one which completes its cycle of operation in one revolution of the crankshaft or in two strokes of the piston. In this engine the function of the intake and exhaust processes of the four stroke engine are taken care by the incoming fresh charge which is compressed either in the crank case or by means of a separate blower while the engine piston is near the bottom dead centre. The engine piston needs only to compress the fresh charge and expand the product of combustion.

In many two stroke engines the mechanical construction is greatly simplified by using the piston as a slide valve in conjunction with intake and exhaust ports cuts in the side of the cylinder. If the engine is running on Otto cycle, the charge consists of correct mixture of fuel and air where as for petrol or duel combustion cycles the charge will consists of pure air.

In 1878, Dugald-clerk, a British engineer introduced a cycle which could be completed in two strokes of the piston rather than as in the case with the four stroke cycle engines.The using this cycle were called two stroke cycle engines. In this engine suction and exhaust strokes are eliminated. Here instead of valves, ports are used. The exhaust gases are driven out from engine cylinder by the fresh charge of fuel entering the cylinder nearly at the end of the working stroke.

HISTORICAL REVIEW

In later development by Day and some other engineers, the automatic valves were eliminated, and all there events controlled by the piston through ports in the cylinder. A deflector is fitted to the piston head with the object (only partially achieved) of directing the fresh mixture upwards and preventing it from escaping or mixing with the exhaust gases. In the "three-port" engine, as it is called, the mechanical system is reduced to the minimum of three working parts, and this has been the pattern for the great majority of two-stroke engines ever since. The diagrams are explanatory only, and not complete or exact in detail, but they are approximately correct in proportions and design of the actual engines.

WORKING OF TWO STROKE PETROL ENGINE

Stroke 1A: Piston at BDCIn the diagram the piston is at BDC (Bottom Dead Centre - meaning it is at the lowest point of travel within the cylinder). The air, petrol and oil mixture within the crankcase is forced into the cylinder and exhaust gases are driven out

Stroke 1B: The Instroke The piston moves upwards and covers the air intake and exhaust ports closing them.

The charge of fresh air is compressed to about 5:1 (20%) of its original volume. The act of compressing the air heats it tremendously.

This happens on every upward stroke of the piston.

Stroke 2A: Piston at TDC Just as the piston reaches the uppermost portion of it's travel at Top Dead Centre (TDC) the spark plug is fired causing combustion of the compressed mixture within the cylinder. At the same time petrol and oil vapour is being drawn into the crank-case in preparation for the next stroke.

Stroke 2B: Piston nearing BDCDuring the downward stroke the exhaust port opens, and the cylinder is swept clean of burnt fuel by fresh air from the inlet port. The petrol, oil and air charge within the crank-case is compressed during this stroke in preparation for the next stroke.

This entire cycle is repeated for every revolution of the crank shaft.

BASIC TEST RIG BLOCK DIAGRAM

PARTS OF TWO STROKE PETROL ENGINE TEST RIG

Engine: The engine ignites fuel at every upward stroke, so there are two strokes for every ignition of fuel. They are called upward and downward stroke. As the piston moves in upward direction from bottom to top in the first stroke the air and fuel mixture gets compressed and ignited by spark plug as upward stroke comes to end. This results in an explosion of mixture which forces the piston to move downwards thereby producing power.

Rope brake dynamometer: rope brake is a simple device for measuring Brake power of an engine. it consists of number of turns of rope wound around the rotating drum attached to the output shaft. one side of the rope is connected to the spring balance and other to the loading device the power absorbed is due to friction between rope and the drum.

Thermocouples: thermocouple is a device mounted on different areas of the engine to measure stroke temperatures.

Engine speed indicator: The function of the speed indicator is to measure the number of revolution per minute of the engine shaft, this is done by using a speed sensor which is displayed in the digital indicator.

Fuel Measuring Device : Fuel tank mounted on sturdy iron stand,burette tube, three way cock, connecting tube & a stop clock.

Air Intake Measurement : Air Intake reservoir of size 0.3mx 0.3m x 0.5 m. with orifice plate, U-Tube manometer of 0.5 m height for the measurement of air flow rate.

SPECIFICATIONS

Engine: Type: 150cc two stroke single cylinder petrol engine Bore diameter: 57mm.

Stroke length: 57mm. Swept volume: 145.45cc.

Compresion ratio: 7.4:1. Max net power: 4.64kw at 5200rpm of

engine. Maximum net torque: 10Nm at 3500rpm.

Rope brake dynamometer: Drum diameter: 200mm.

Rope diameter: 24mm. Spring balance: Up to 5kgs.

USE OF THE TEST RIG

The engine performance is indicated by the term efficiency, η. Five important engine efficiencies and other related engine performance parameters are given below:

Indicated thermal efficiency Brake thermal efficiency Mechanical efficiency Volumetric efficiency Relative efficiency or efficiency ratio

Mean effective pressure Mean piston speed Specific power output Specific fuel consumption Fuel-air or air-fuel ratio Calorific value of the fuel

SCOPE AND APPLICATIONS

As there is a working stroke for each revolution, the power developed will be nearly twice that of a four stroke engine of the same dimensions and operating at the same speed.

The work required to overcome the friction of the exhaust and suction strokes is saved.

Two stroke engines are lighter than four stroke engines for the same power output and speed.

For the same output, two stroke engines occupy lesser space.

In case of two stroke engines because of scavenging, burnt gases do not remain in the clearance space as in case of four stroke engines.

The construction of a two stroke cycle engine is simpler because it has ports instead of valves. This reduces the maintenance problems considerably.

APPOXIMATE COST ESTIMATION

ENGINE Rs.3600/- ENGINE BED Rs.1500/- ROPE BRAKE DYNAMOMETER Rs.5000/- TEMPERATURE INDICATORS(RTD) Rs.5000/- SPEEDOMETER(DIGITAL) Rs.3500/- AIR BOX AND FUEL TANK Rs.1500/- BEARINGS AND COUPLING Rs.1200/- OTHER MOUNTINGS Rs.4000/- TABLE Rs.2000/- FABRICATIONS Rs.5000/-

TOTAL Rs.32300-/

CONCLUSION

We want to build up this project for our college laboratory purpose to study the performance of two stroke petrol engine at various loading at environmental conditions.

We ensure that the project will get completed in time and we will give our full effort to make it successful.

Thanking you