Harish-Chandra transform

Engine Testing

With a growing demand for transportation IC engines have gained lot of importance in automobile industry. It is therefore necessary to produce efficient and economical engines. While developing an IC engine it is required to take in consideration all the parameters affecting the engines design and performance. There are enormous parameters so it becomes difficult to account them while designing an engine. So it becomes necessary to conduct tests on the engine and determine the measures to be taken to improve the engines performance.

Performance parameters

1. Power and Mechanical Efficiency

2. Fuel Air-Ratio

3. Volumetric Efficiency

4. Specific Output

5. Specific Fuel Consumption

6. Thermal Efficiency and Heat Balance

7. Exhaust Smoke and Emissions

8. Effective Pressure and Torque

Power and mechanical efficiency

An IC engine is used to produce mechanical power by combustion of fuel. Power is referred to as the rate at which work is done. Power is expressed as the product of force and linear velocity or product of torque and angular velocity. In order to measure power one needs to measure torque or force and speed. The force or torque is measured by Dynamometer and speed by Tachometer. The power developed by an engine and measured at the output shaft is called the brake power (bp) and is given by,

$bp=\frac{2\pi N\tau }{60}$

where:

$\tau$ is the torque,

$N$ is the rotational speed,

However while calculating the Mechanical efficiency another factor called Indicated power is considered. It is defined as the power developed by combustion of fuel in the combustion chamber (ip). It is always more than brake power. It is given by,

$ip=\frac{pARk}{60}$

where:

$p$ is the mean pressure,

$A$ is the area of the piston

$k$ is the number of cylinders

Therefore the difference between ip and bp indicates the power loss in the mechanical components of engine(due to friction). So the mechanical efficiency is defined as ratio of brake power to the indicated power.

$E=\frac{bp}{ip}$ or  :$E=\frac{bp}{bp+fp}$

Friction power is the difference between indicated power and brake power.

$fp=ip-bp$

Fuel-air ratio

Fuel-Air Ratio Test

It is the ratio of mass of fuel to mass of air in mixture. It effects the phenomenon of combustion and used for determining flame propagation velocity, the heat released in combustion chamber. For practise always relative fuel air ratio is defined. It is the ratio of actual fuel-air ratio to that of the stoichiometric fuel air ratio required for burning of fuel which is supplied.

Relative fuel-air ratio, :$(F/A)=\frac{Actualfuel-airratio}{stoichiometricfuel-airratio}$

Thermal efficiency and heat balance

It is the ratio of output to that of energy input in the form of fuel. It gives the efficiency with which the chemical energy of fuel is converted into mechanical work. It shows that all chemical energy of fuel is not converted into heat energy.

Thermal efficiency and total energy input- The methodology for calculating thermal efficiency of a unit is described in this section to help to determine whether the unit qualifies to exemption or not. It also includes total energy input which also helps in determining thermal efficiency.

The thermal efficiency standard for a unit are decided by CAIR model trading rules, the CAIR FIP, CAMR, the CAMR Hg model trading rule, and the proposed CAMR Federal Plan, EPA. However,the thermal efficiency standard applicable to all fuels combusted by a unit are decided by the United States Environmental Protection Agency (EPA), while the application of the standard to natural gas and oil are made by FERC.

Brake specific fuel consumption(bsfc)

It is defined as the amount of fuel consumed for each unit of brake power per hour it indicates the efficiency with which the engine develops the power from fuel. it is used to compare performance of different engines.

The amount of fuel which an engine consumes is rated by its BRAKE SPECIFIC FUEL CONSUMPTION (BSFC). In the U.S. this is generally computed in dimensions of pounds of fuel per horsepower per hour. For most internal combustion engines the BSFC will be in the range of 0.5 to 0.6. This estimate fits well with the old rule of thumb that an engine will burn HP/10 gallons per hour. Here is an example with a 90-HP engine. When developing 90-HP, how much fuel will it burn? Assume a BSFC of 0.55 and gasoline at 6.25 lbs/gallon: 90 x 0.55 = 49.5 pounds of fuel burned per hour 49.5 x 1/6.25 = 7.92 gallons per hour

The fuel efficiency will tend to peak at higher engine speeds. At near wide open throttle the BSFC will be closer to a value of 0.5. The BSFC tends to be the same for similar engines. Really huge diesel engines have reported BSFC values in the 0.35 range. The estimate of brake specific fuel consumption for two-stroke engines ranges from 0.55 to as high as 0.8 pounds of fuel per horsepower per hour. I have a 1992 Evinrude V6 loop-scavenged 225-HP two-stroke which is in good tune and for which I have some fuel consumption data. From this I try to estimate my engine's BSFC

Measurement of brake power

Britannica Dynamometer 1

The torque and the angular speed measurement of engine are involved in measurement of break power. Dynamometer is used for torque measurement. The rotor of the engine which is under state is connected to stator. Rotor moves through distance 2πr against force F. Hence work done,

$W=2\pi rF$

They are of two types-

Absorption dynamometer

It absorbs and measures output power of engine. This power is dissipated in the form of heat. e.g., prony brake, hydraulic dynamometer, rope dynamometer, eddy current dynamometer, swinging field d.c. dynamometer etc. Absorption dynamometers are ideally suited for testing petrol engines for mopeds and electrical F.H.P. motors. Their main advantage lies in the fact that they are self aircooled and hence water cooling or additional air cooling is not required. This advantage is particularly significant in case of moped engines and F.H.P. motors, which are also air cooled.

Transmission dynamometer

In this the power is transmitted to load connected to engine. Torque meter is alternative name of this dynamometer. It is usually consist of strain gauge which measures the torque by angular deformation of shaft. These dynamometers are accurate and widely used in automatic units. It is available in both electric motor and hydrostatically-driven versions, the AIDCO Model 450E and 450 Transmission Dynamometer Test Stands are designed for automatic transmission dyno testing and for testing power shift transmissions used in commercial applications built by Allison, ZF, Voith, and Renk, as well as most military transmissions.

Exhaust smoke and other emission

Exhaust Emission Test

Smoke and other emission are undesirable for public environment. Due to global warming and emphasis on air pollution all possible things are tried to keep them low. Smoke also indicates incomplete combustion of fuel.

Practical solutions for reduce air pollution-

•There have been very few solutions made available that are both cost-effective and efficient regardless of health complicated issues. •Gives protection of firemen, children and other public workers who are exposed to harmful gases. •No loss mileage or horsepower in engine. •Does not use engine resources to operate. •Installation and compatible of all diesel engines are easy, which quickly solves the root of the problem. •Prolonged filter and maintenance are easy, which automatically triggers diesel emission filtration. •Shielding yourself by providing legal safe workplace. •Effective on high octane low sulphur diesel fuel or ordinary fuel. • Reduction in 99% diesel emission.

Mean effective pressure and torque

Mean effective pressure is an important parameter for comparing the performance of different engines. It is defined as the average pressure acting over piston throughout a power stroke. It is given by the following relation,

$p=\frac{ip60}{LARK}$

where:

$p$ is the Mean Effective Pressure,

$ip$ is Indicated Power

e Indicated power watt

$A$ is the Area of the Piston

$R$ is the Rotational Speed

$k$ is the Number of Cylinders,

If mean effective pressure is based on brake power(bp) then it is referred to as brake mean effective pressure(bmep). If it is based on indicated power(ip) it is called indicated mean effective pressure(imep). friction mean effective power is the difference of imep and bmep,

$fmep=imep-bmep$

Mean effective pressure also has an effect on torque. Torque could be expressed by following relation also

$\tau =\frac{bmepARK}{2\pi }$

Mean effective pressure and torque both are affected by the size of engine. A large engine produces more Torque for the same mean effective pressure. For this reason engines mean effective pressure gives indication of its displacement utilization and not torque. Power of an engine is dependent on its size so it is not possible to compare different engines based on their power or torque. Therefore Mean effective pressure is the true indication of the relative performance of different engines.

Volumetric efficiency

It is the ratio of the actual volume of the charge drawn in during the suction stroke to the swept volume of the piston.The amount of air taken inside the cylinder is dependent on the volumetric efficiency of an engine and hence puts a limit on the amount of fuel which can be efficiently burned and the power output. The value of volumetric efficiency of a normal engine lies between 70 to 80 percent, but for engines with forced induction it may be more than 100 percent.

References

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.