Week 2 : Basic Calibration of Single cylinder SI-Engine

TARGET:

• To run a single cylinder petrol engine setup at 1800rpm and give parameters like air flow, BSFC, BMEP, cylinder pressure.
• Run the same setup at 3600rpm and increase power by 10%

INTRODUCTION:

An internal combustion engine (SI engine) is an internal combustion engine, generally a gasoline engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to diesel engines, typically diesel engines, where the heat generated by compression along with fuel injection is sufficient to initiate the combustion process without the need for any external spark.

HOW THE ENGINE WORKS:

The duty cycle of both petrol and diesel engines can be two-stroke or four-stroke.

A four-stroke gasoline engine is an ottocycle engine. It consists of the following four strokes: intake or intake stroke, compression stroke, expansion or power stroke, exhaust stroke. Each stroke consists of a 180-degree rotation of the crankshaft, and therefore the four-stroke cycle is completed through a 720-degree rotation of the crank. Thus, there is only one power stroke per complete cycle, while the crankshaft rotates two or more revolutions.

 

The air-fuel ratio (AFR) is the mass ratio of air to the solid, liquid, or gaseous fuel present in the combustion process. Combustion can occur in a controlled manner, such as in an internal combustion engine or industrial furnace, or it can lead to an explosion (eg, a dust explosion, gas or vapor explosion, or in a thermobaric weapon).

The air-fuel ratio determines whether the mixture is flammable at all, how much energy is released, and how many unwanted pollutants are produced during the reaction. Typically, there is a range of fuel/air ratios beyond which ignition will not occur. These are known as the lower and upper explosive limits.

In internal combustion engines or industrial furnaces, the air-fuel ratio is an important measure for pollution protection and performance tuning reasons. If exactly enough air is provided to burn all the fuel completely, the ratio is known as the stoichiometric mixture, often abbreviated to stoichi. Ratios less than stoichiometric are considered "rich". Rich mixtures are less efficient, but can produce more power and burn cooler. Ratios higher than stoichiometric are considered "lean". Lean mixtures are more efficient, but can cause higher temperatures, which can lead to the formation of nitrogen oxides. Some engines are designed with lean burn features. For accurate calculations of the air-fuel ratio, the oxygen content of the combustion air should be specified due to different air density due to different altitude or intake air temperature, possible dilution by ambient water vapor or enrichment by added oxygen.

In theory, the stoichiometric mixture has just enough air to completely burn the available fuel. In practice, this is never fully achieved, mainly due to the very short time available to the internal combustion engine for each combustion cycle. Most of the combustion process is completed in about 2 milliseconds at an engine speed of 6,000 rpm. (100 revolutions per second; 10 milliseconds per crankshaft revolution - which for a four-stroke engine would typically mean 5 milliseconds for each piston stroke). This is the time that elapses from ignition of the spark plug until 90% of the fuel-air mixture is burned, usually about 80 degrees of crankshaft rotation later. Catalytic converters are designed to work best when the exhaust gases passing through them are the result of near-perfect combustion.

1.Run the case at 1800 rpm and list down important parameters

• air flow rate
• BMEP
• BSFC
• In-cylinder pressure

The model is imported from tutorials > modelling applications > engine_performance > 1cylSi-final.gtm

        

1. AIR FLOW RATE:

        

        Air flow rate: 24.6 kg/h

2. BRAKE MEAN EFFECTIVE PRESSURE:

        

        Break mean effective pressure: 9.5 bar

3. BRAKE SPECIFIC FUEL CONSUMPTION:

        

        Brake specific fuel consumption: 239.2 g/kw-h

4. IN-CYLINDER PRESSURE:

        

       In-cylinder pressure: 48.89 bar

RUNNING THE ENGINE AT 3600 RPM:

        

        Brake power output: 16.7 KW

INCREASING THE POWER OUTPUT BY 10%:

The output power can be increased by changing the various parameters,

• By increasing the bore
• By increasing the stroke
• By increasing bore, stroke and connecting rod
• By increasing inlet pressure

• In case 1, RPM is changed from 1800 to 3600 RPM.
• In case 2, bore is changed from 86 to 90 mm.
• In case 3, stroke is changed from 86 to 96 mm
• In case 4, bore is changed from 86 to 88 mm, stroke is changed from 86 to 90 mm and connecting rod length is changed from 175 to 180mm.
• In case 5, intake pressure is changed from 1 to 1.1 bar.

RESULTS:

 

By changing the inputs as above, the braking power obtained increases by 10% at a constant speed of 3600 rpm.

• In case 1, the braking power obtained is 16.7 kW.
• In case 2, the obtained braking power is 18.4 kW.
• In case 3, the obtained braking power is 18.6 kW.
• In case 4, the obtained braking power is 18.3 kW.
• In case 5, the obtained braking power is 18.9 kW.

CONCLUSION:

• By increasing the volume of the cylinder by changing the bore and stroke, more air and can of fuel are burned.
• By increasing the length of the connecting rod, better torque can be achieved.
• By increasing the intake pressure, better combustion can be achieved, but increasing the intake air pressure requires a turbocharger or supercharger, which increases the cost of the engine.

The above steps will increase the engine power by 10%.