Challenge

Week 2 : Basic Calibration of Single cylinder SI-Engine

FFaizan Akhtar22 Oct 2021

Aim: Basic Calibration of Single-cylinder SI-Engine

Objective:

1. Run the case at 1800 rpm and list down important parameters (20 Marks)

air flow rate
BMEP
BSFC
In-cylinder pressure

2. Increase the power output at 3600 rpm by 10% (30 Marks)

Introduction

A spark-ignition engine (SI engine) is an internal combustion engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to CI, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.

Working of SI engine

1. Suction Stroke

In this stroke, the piston moves downward, and the air-fuel mixture from the carburetor enters into the cylinder through the inlet valve. During this stroke inlet valve opens and the exhaust valve remains closed.

2. Compression Stroke

In this stroke, the piston moves upward and compresses the air-fuel mixture. The compression strokes complete as the piston moves at TDC. During this stroke, Both the inlet and exhaust valve remains closed.

3. Power Stroke

At the end of the compression stroke, a spark is produced by the spark plug. This spark ignites the air-fuel mixture and combustion takes place in the combustion chamber. Due to combustion, a very high thrust force is generated which pushes the piston downward rapidly and makes the crankshaft rotate. This stroke is called a power stroke because we get power in it. Both inlet and exhaust valve remains closed in this stroke.

4. Exhaust Stroke

In this stroke, the piston moves upward and burnt or exhaust gases produced in the power stroke escape out of the cylinder through the exhaust valve. In this stroke, the exhaust valve gets open and the inlet valve remains closed.

Air fuel ratio

Air–fuel ratio (AFR) is the mass ratio of air to a solid, liquid, or gaseous fuel present in a combustion process. The combustion may take place in a controlled manner such as in an IC Engine or industrial furnace or may result in an explosion.

The air-fuel ratio determines whether a mixture is combustible at all, how much energy is being released, and how many unwanted pollutants are produced in the reaction. Typically a range of fuel to air ratios exists, outside of which ignition will not occur. These are known as the lower and upper explosive limits.

In an IC Engine or industrial furnace, the air-fuel ratio is an important measure for anti-pollution and performance-tuning reasons. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture. Ratios lower than stoichiometric are considered "rich." Rich mixtures are less efficient, but may produce more power and burn cooler. Ratios higher than stoichiometric are considered "lean." Lean mixtures are more efficient but may cause higher temperatures, which can lead to the formation of nitrogen oxides. Some engines are designed with features to allow lean burn. For precise air-fuel ratio calculations, the oxygen content of combustion air should be specified because of different air densities due to different altitude or intake air temperatures, possible dilution by ambient water vapor, or enrichment by oxygen additions.