Performance Characteristics of Spark ignition

Internal Combustion Engine.

 

The Purpose of the Experiment

This experiment’s objective is to study the engine performance characteristics, such as brake power, torque, brake-specific fuel consumption, etc., under different engine loading conditions using a hydraulic dynamometer coupled to a single-cylinder petrol engine.

 

1.0 Introduction

Reciprocating internal combustion (IC) engine has become the most used engine as per today. Spark-ignition (SI) gasoline/petrol engine is an example of an internal combustion engine used today to transport vehicles in the automobile industry. Despite all this, the use of petrol/gasoline engines is being outdone since it has caused some major environmental impacts, hazardous to the ecosystem [1].

A Reciprocating engine consists of:

• Engine block,
• Cylinder head,
• Piston and piston pin,
• Connecting rod,
• Crankshaft, flywheel,
• Valves and valve mechanisms and camshaft

 

Petroleum is getting depleted; this has raised the need for some other sources of fuels. Despite enough research works, CNG and Hydrogen have been used in recent designs to optimize fuel use. Mixing it with petrol/gasoline has been proved to give wonderful results such as reduced fuel use and creating a more friendly environment [2].

A single-cylinder petrol engine’s performance is evaluated using an engine testbed and coupled with a dynamometer in this lab work. The engine dynamometer measures the engine’s output. The engine dynamometer will engage the torque and power levels while regulating the engine speed to allow the occurrence of performance assessment.

2.0 Theory

There are two operations modes of an internal combustion engine; a 4-stroke cycle or a 2-stroke Spark ignition petrol engine operates with a 4-stroke cycle. This means that there are 4 piston strokes in a cyclic thermodynamic process  [5].

 

2.1. Theory of IC Engines.

The piston has to go through only 2 strokes to make a full cycle. Because of this, the 2-stroke engine is more advantageous. However, since the 2 strokes, the IC engine has high speeds, it is inefficient in gas exchange processes than 4 stroke engines. The 2-stroke cycle is applied in marine type large and slow CI engines.  Its also applied in light SI engines used on lawnmowers and motorcycles. There are 2 strokes cycle CI engines with power between 200-500 kW working with an estimated speed of 2000 rpm [3].

 

 

2.1 Brake Power (bp)

Engine’s horsepower without the loss in power can be caused by the generator, gearbox, water pump, differential, and other auxiliaries.

 

………………………………                    equation 1

Where bp= Brake power (W)  T=Torque (Nm)           N = Engine Speed (rpm)

 

2.2 Brake specific fuel consumption (BSFC)

This entails measuring any prime mover’s fuel efficiency that burns fuel and produces rotational, or shaft, power. Its purpose is to compare the internal combustion’s efficiency with a shaft output. The formula used for its calculation is:

 

……………………

2.3 Brake thermal efficiency

This is the brake power of an engine taken as a function of the fuel’s thermal input. Its work is to evaluate the ability of an engine to convert heat from fuel to mechanical energy.

 

…………………..

 

6.4. Brake Mean Effective Pressure (BMEP).

Although it is a measure of an engine’s ability to do work, torque cannot be used to compare Torque cannot be used to different engines because of its dependence on engine size. Dividing the work per cycle by the volume of the cylinder displaced per cycle gives a reliable measure for engine characteristics. This parameter is called brake mean effective pressure; it is defined as the mean pressure which the gas exerts on the piston via a complete operating cycle.

Where bmep = Brake Mean Effective Pressure (kPa)

N_bc = Corrected brake power (kW)

n = Engine speed (rev/sec)

j = Number of strokes

i = number of cylinders

Vs = Swept volume of a single cylinder (m3)

6.5 Actual Air-Fuel Ratio

The fuel mass flow and air values found from reading the airflow manometer give the actual air-fuel ratio.

 6.6. Volumetric Efficiency

This is the ratio of the amount of air-fuel mixture entering the cylinder to the amount that could enter when in ideal standard atmospheric conditions.

Where ηv = Volumetric Efficiency (%)

= Actual Air Flow Rate (kg/s) m

= Theoretical Air Flow Rate (kg/s)

The four-stroke engine cycle.

Figure 1.The 4 strokes of a diesel engine

  The diesel cycle-The assumption made before doing any diesel cycle analysis are;

1. During the suction stroke and the exhaust stroke, the air pressure and the products are the atmospheric pressure, i.e., there is no ‘pumping loss.’
2. That all the cycle’s operations are adiabatic.
3. That the fuel’s combustion occurs at constant pressure, meaning the line 2-3 is horizontal;
4. That, the fuel is totally boiled away before getting into the cylinder, for liquid fuel.
5. That the compressed air is pumped into the cylinder at the temperature T 1 without compressed air.

• 0-1: ISOBARIC(INDUCTION=1bar)
• 1-2: ADIABATIC(COMPRESSION)
• 2-3: ISOCHORIC(IGNITION)
• 3-4: ADIABATIC(EXANSION)

 

Figure 2 Indicator diagram of an ideal Diesel Engine.

Line 0-1 shows air entrance to the cylinder during the 1st stroke. Curve 1-2 shows the compression of the air during the return stroke. The fuel is forced into the cylinder and ignites because of high temperatures at 2. Fuel supply goes on as the piston moves back, which leads to burning at constant pressure. Curvature 3-4 gives the characterization of the adiabatic expansion of the combustion products. The exhaust valve opens at point 4, causing the products to outflow the cylinder. A fraction of the gas mixture is enforced via the exhaust valve in the fourth stroke; Part of the mixture will remain in the clearance space and gets mixed with the incoming air. [3].

 

 

 

 

 

3.0 Requirements/Apparatus/Equipment. 

• Type: – Single cylinder, twin overhead-valve, 4-stroke petrol engine.
• Fuel: – Petrol of minimum 90 RON.
• Fuel supply: – Gravity fed conventional carburetor with manual choke and the mechanical governor to regulate maximum speed.
• Ignition: – Spark plug via a permanent magnet and coil induction.
• Starter: – Cord and handle recoil starter.
• Engine internals
  • Capacity 208cc
  • Bore 70mm
  • Stroke/crank radius 54mm / 27mm
  • Connecting rod length 84mm
  • Compression ratio 8.5:1
  • Oil Capacity 0.6 liter
  • Exhaust outlet (nominal) 1” BSP
• Max Power 5.2kW (7hp) at 3600rpm (without air cleaner and exhaust).
• Net Power 4.5kW at 3600rpm
• 2kW at 1800rpm
• Airbox inlet orifice 18.49mm

 

 

4.0 Results and discussion

TORQUE Vs. ENGINE SPEED.

The engine torque increases with an increase in the engine speed from the graph above until around 13.8 Nm, where the torque decreases steeply.

POWER Vs. ENGINE SPEED.

An increase in speed leads to a proportional increase in the engine’s power until about 3190W, where it reaches maximum power, and a further increase in speed leads to a drop in power.

 

 

 

 

 

 

 

 

 

 

Air Fuel Ratio

Air fuel ratio is reduced with an increase in speed until about 11.00, where it increases gradually.

 

 

 

Specific Consumption (kg.kWh-1 ) Vs Speed

 

The specific consumption slowly increases as if wanting to flatten with a constant value at the engine speed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Thermal Efficiency (%) Vs. Speed(RPM

 

Thermal efficiency is constant at the start of the engine’s speed and decreases thereafter.

 

Volumetric Efficiency (%) vs. Speed (RPM)

 

The volumetric efficiency is constant at the start but decreases with an increase in engine speed.

Exhaust Gas Temperature (°C) Vs. Speed(RPM)

 

An increase in engine speed leads to an increase in exhaust gas temperature.

Calculated Torque

Nm

Calculated Parameters (Engine)

• Air Fuel Ratio

 

• Specific Consumption

 

 

• Thermal Efficiency

If =0.00026kg/s, fuel calorific value is 43.8 x 10^6 J/Kg and the brake power is 2680 W

The  =23.53%

• (Break Mean Effective Pressure) BMEP

 

=4.99bar

Calculated parameters

Calculated Parameters (Energy)
Heat Of Combustion	Inlet Air Enthalpy
(W)	(W)
11388	1046
12264	900
8760	732
6570	614
6132	551
6132	571
5694	563
6132	606
5694	543
5694	620

 

Calculated Parameters (Engine)
Air Fuel Ratio	Specific Consumption	Thermal Efficiency	Volumetric Efficiency	Engine Capacity	Number Of Cycles [2 or 4]	BMEP
	(kg.kWh-1)	(%)	(%)	(cc)		(bar)
14.15	0.35	23.53	54.80	200	4	4.99
11.32	0.32	26.01	66.61	200	4	8.39
12.90	0.31	26.56	69.40	200	4	7.84
14.40	0.29	28.25	69.05	200	4	7.42
13.86	0.31	26.17	66.75	200	4	6.91
14.36	0.31	26.34	68.40	200	4	6.88
15.23	0.28	29.03	67.43	200	4	7.04
15.21	0.32	25.51	73.65	200	4	6.76
15.23	0.30	27.77	65.77	200	4	6.81
16.77	0.30	27.41	75.30	200	4	6.73

 

 

 

 

Conclusion

The possible sources of errors encountered during this experiment are:

• The use of a chronometer or a watch might have led to incorrect timings causing variations in the data collected.
• The lab’s ambient temperature conditions can vary at different times of the day, hence giving results variations or on various weather conditions.
• Reading water vapor pressures in thermodynamic tables might be accompanied by errors when different done under varying weather conditions and times of the day.

 

 

References

[1]	Ankit Sonthalia, Chidambaram Ramesh Kumar, Anirudh S Punganur, “Combustion and Performance Characteristics of a Small Spark-Ignition Fuelled with HCNG,” Journal of Engineering Science and Technology, vol. 10(4), p. 405, May 2015.
[2]	Wang, J.; Huang, Z.; Fang, Y.; Liu, B.; Zeng, K.; and Miao, H., “Combustion behaviors of a direct-injection engine operating on various fractions of natural gas hydrogen blends.,” International Journal of Hydrogen Energy, vol. 32(15), pp. 3555-3564, 2007.
[3]	TD110-TD115 testbed and instrumentation for small, Workshop Manual, 2004.
[4]	J. Heywood, Internal combustion engine fundamentals, McGraw-hill, (1988).
[5]	G. A. GOODENOUGH, A Thermodynamic Analysis of Internal -Combustion Engine Cycles, Urbana, Illinois: UNIVERSITY OF ILLINOIS, URBANA, 1927.
[6]	D. Ellis, Thermofluids & Turbomachinery: IC engine performance, 2012.