What is Engine Cycle ?

The term "engine cycle" typically refers to the sequence of events that occur within an internal combustion engine during one complete operation. There are several types of engine cycles, but the most common ones are the Otto cycle and the Diesel cycle.

1. Otto Cycle: This is the cycle used in gasoline engines. It consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing the air-fuel mixture to enter the combustion chamber as the piston moves down.
   • Compression Stroke: Both intake and exhaust valves close, and the piston moves up, compressing the air-fuel mixture.
   • Power Stroke: When the air-fuel mixture is compressed, a spark plug ignites it, causing an explosion that drives the piston down, producing power.
   • Exhaust Stroke: Finally, the exhaust valve opens, and the piston moves up, pushing the burnt gases out of the combustion chamber.

2. Diesel Cycle: This cycle is used in diesel engines and is similar to the Otto cycle but differs in the method of ignition. It also consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing air into the cylinder.
   • Compression Stroke: The air is compressed highly, raising its temperature. Fuel is then injected directly into the cylinder near the top of the compression stroke.
   • Power Stroke: The injected fuel ignites due to the high temperature of the compressed air, driving the piston down.
   • Exhaust Stroke: The exhaust valve opens, and the piston moves up, expelling the exhaust gases.

These cycles are fundamental to the operation of internal combustion engines and are the basis for the efficiency and performance characteristics of various engine designs.

Standard diesel engine cycle

The standard diesel engine cycle, also known as the Diesel cycle, is a theoretical thermodynamic cycle that represents the operation of a diesel engine. It was first proposed by Rudolf Diesel, the inventor of the diesel engine. The Diesel cycle consists of four distinct processes:

1. Intake Stroke: The intake valve opens, and fresh air is drawn into the cylinder as the piston moves downward. Unlike in gasoline engines, no fuel is introduced during this stroke.

2. Compression Stroke: Once the intake valve closes, the piston moves upward, compressing the air within the cylinder. This compression process raises the temperature of the air significantly, typically to temperatures high enough to ignite diesel fuel.

3. Power Stroke: Near the top of the compression stroke, fuel is injected into the highly compressed, hot air. The fuel instantly ignites due to the high temperature, causing rapid combustion and an increase in pressure within the cylinder. This pressure forces the piston downward, producing power.

4. Exhaust Stroke: As the piston reaches the bottom of its stroke, the exhaust valve opens, and the piston moves upward again, pushing the burnt gases out of the cylinder.

The Diesel cycle is characterized by constant-pressure heat addition (combustion) and constant-volume heat rejection (exhaust). This cycle is different from the Otto cycle, which is used in gasoline engines, primarily in the method of ignition—diesel engines rely on the heat generated by compression to ignite the fuel, while gasoline engines use spark plugs for ignition. Diesel engines are known for their high efficiency and torque output, making them popular in applications such as heavy-duty trucks, buses, and industrial machinery.

The difference between TBN and TAN

TBN (Total Base Number) and TAN (Total Acid Number) are both measures used in the analysis of lubricants and oils, particularly in engines, to assess their condition and performance. However, they represent different aspects of the oil chemistry:

1. Total Base Number (TBN):

   • TBN measures the reserve alkalinity of an oil, indicating its ability to neutralize acids formed during the combustion process in an engine.
   • It represents the amount of alkaline additives, such as detergents and dispersants, present in the oil to counteract the acidic by-products of combustion and chemical degradation.
   • Higher TBN values indicate greater acid-neutralizing capability and, therefore, better protection against corrosion and wear caused by acidic compounds.

2. Total Acid Number (TAN):

   • TAN measures the acidity of an oil, specifically the amount of acidic components present in the oil due to oxidation, thermal degradation, and contamination.
   • It reflects the concentration of acidic contaminants, such as oxidation products, organic acids, and inorganic acids, which can corrode engine components and degrade the lubricating properties of the oil.
   • Increasing TAN values indicate higher levels of acidic compounds and potential degradation of the oil, which may necessitate oil changes or other maintenance actions to prevent engine damage.

In summary, while TBN indicates the alkaline reserve of an oil to neutralize acids, TAN measures the actual acidity level of the oil due to various factors. Monitoring both TBN and TAN is essential for assessing the condition and performance of lubricants and oils in engine applications, helping to ensure proper lubrication and prolonging the life of engine components.

TBN In Diesel Engine Oils

In diesel engine oils, Total Base Number (TBN) plays a critical role in maintaining engine health and performance. Here's why TBN is significant in diesel engine oils:

1. Neutralization of Acids: During the combustion process in a diesel engine, various acidic by-products are formed, including sulfuric acid and other acidic compounds. These acids can lead to corrosion of engine components and degradation of the oil's lubricating properties. The TBN of the oil indicates its ability to neutralize these acidic compounds, thereby preventing corrosion and maintaining oil stability.

2. Protection Against Wear: Acidic compounds can accelerate wear on engine parts, such as piston rings, cylinder liners, and bearings. By neutralizing these acids, diesel engine oils with a sufficient TBN help protect critical engine components from premature wear and extend their service life.

3. Extended Drain Intervals: The TBN of diesel engine oils influences the recommended oil change intervals. Oils with higher TBN values typically have greater acid-neutralizing capacity and can maintain their effectiveness for a longer period, allowing for extended drain intervals. This can result in cost savings and reduced maintenance downtime for diesel engine operators.

4. Performance in High-Sulfur Environments: Diesel fuels with higher sulfur content can lead to increased formation of acidic by-products during combustion. Engine oils with higher TBN values are better equipped to handle these conditions, providing enhanced protection against corrosion and maintaining oil stability in high-sulfur environments.

5. Oil Condition Monitoring: Regular monitoring of TBN levels is essential for assessing the health and effectiveness of diesel engine oils. TBN analysis helps determine when the oil's acid-neutralizing capacity is depleted, indicating the need for an oil change to prevent potential engine damage.

In summary, TBN is a crucial parameter in diesel engine oils, providing protection against acidic corrosion, minimizing wear on engine components, extending oil change intervals, and ensuring optimal engine performance, particularly in challenging operating environments with high sulfur content.