Unit: 4
IC Engine and cycle
An internal combustion (IC) engine is a type of heat engine in which combustion (burning of fuel) occurs within the engine itself, as opposed to an external source of heat. The four-stroke cycle is the most common type of IC engine cycle. It consists of four stages: intake, compression, power, and exhaust. During the intake stage, fuel and air are drawn into the cylinder. During compression, the mixture is compressed, increasing its temperature and pressure.
In the power stage, the compressed mixture is ignited, causing combustion and generating power. Finally, in the exhaust stage, the spent combustion products are expelled from the cylinder. Other IC engine cycles include the two-stroke cycle and the diesel cycle.
A/f Ratio :
The air-fuel ratio (AFR) or air-fuel mixture is the mass ratio of air to fuel present in a combustion process. The AFR is an important parameter in internal combustion engines, as it has a significant effect on engine performance, emissions and combustion efficiency.
A stoichiometric AFR for gasoline is 14.7:1, meaning for every 14.7 parts of air, one part of fuel is required for complete combustion. If the AFR is leaner (more air and less fuel) than stoichiometric, the engine will tend to have better fuel efficiency, but may experience less power output, increased combustion chamber temperatures, and increased emissions of nitrogen oxides (NOx). If the AFR is richer (more fuel and less air) than stoichiometric, the engine will tend to produce more power, but may experience increased emissions of hydrocarbons (HC) and carbon monoxide (CO), and reduced fuel efficiency.
It's important to note that the stoichiometric AFR may vary depending on the fuel type and engine design, also a common AFR in diesel engines is around 14.6:1
Sources Of Air Pollutants :
Air pollutants can come from a variety of sources, including natural and human-made sources. Some common sources of air pollutants include:
Industrial Facilities: Factories, power plants, and other industrial facilities release pollutants into the air through the burning of fossil fuels, such as coal, oil, and natural gas, and through chemical processes.
Transportation: Cars, trucks, buses, and airplanes emit pollutants into the air, including nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter (PM).
Agriculture: Livestock farming and the use of pesticides and fertilizers in agriculture can contribute to air pollution.
Residential and commercial: The use of heating and cooling systems, fireplaces, and other equipment in homes and buildings can release pollutants into the air.
Natural sources: Forest fires, volcanic eruptions, and dust storms can release pollutants into the air.
Waste management: Landfills and waste incineration facilities can release pollutants into the air.
Construction: Dust and emissions generated by construction equipment and vehicles can contribute to air pollution.
It's important to note that these sources can vary depending on the location and the regulations in place to control the emissions.
Control By Process Change :
Control of air pollution through process changes involves making changes to the way a facility or process operates in order to reduce the emissions of pollutants into the air. Some examples of process changes that can be used to control air pollution include:
Substitution: Replacing a pollutant-emitting material or process with a less polluting alternative. For example, replacing fossil fuels with renewable energy sources such as solar or wind power.
Modification: Making changes to a process or equipment to reduce emissions. For example, installing scrubbers on power plant smokestacks to remove sulfur dioxide (SO2) emissions.
Add-on control: Adding equipment or technology to a process to control emissions. For example, installing catalytic converters on vehicles to reduce emissions of nitrogen oxides (NOx) and hydrocarbons (HC).
Process modification: Changing the way a process operates to reduce emissions. For example, increasing the efficiency of an industrial furnace to reduce the amount of fuel needed and thus the emissions of pollutants.
Improved maintenance: Regular maintenance of equipment and processes can help to ensure they are operating correctly and efficiently, reducing emissions of pollutants.
These process changes can be implemented through different regulations and policies, such as emissions standards, permit system, and taxes. Additionally, it's important to note that process changes can also have an impact on the economy, some of them can be costly, but in the long run, they can be beneficial for the health and the environment.
Engine Design Change
Engine design changes can be implemented for various reasons such as improving performance, increasing fuel efficiency, reducing emissions, increasing reliability and durability, and reducing manufacturing costs. These changes can include modifications to the engine's layout, the materials used, or the specific components and systems within the engine. The process of implementing an engine design change typically involves a detailed design and development phase, followed by testing and validation. The final design must meet the required performance and safety standards before it can be put into production.
Stratified charge engines are a type of internal combustion engine that use a specific combustion chamber design to improve the engine's efficiency and reduce emissions. The basic concept of a stratified charge engine is that the fuel and air are not well mixed, as in a conventional engine, but are instead separated into distinct layers or "strata." This allows for a leaner fuel-air mixture in the combustion chamber, which can result in a more complete combustion and higher thermal efficiency.
There are different types of stratified charge engine designs, but some common ones include:
Direct Injection Stratified Charge (DISC) engines, where fuel is directly injected into the combustion chamber
Controlled Auto-Ignition (CAI) engines, also known as Homogeneous Charge Compression Ignition (HCCI) engines, where the fuel and air are injected into the combustion chamber in a homogeneous mixture and then compressed to a point where the mixture auto-ignites.
Stratified charge engines are more complex than conventional engines, and require advanced control systems to properly manage the fuel-air mixture. However, they offer the potential for significant improvements in fuel efficiency and reduced emissions, making them an area of ongoing research and development.
Rotary Combustion Engine :
A rotary combustion engine, also known as a rotary engine or Wankel engine, is a type of internal combustion engine that uses a rotary design instead of the traditional reciprocating design. In a rotary engine, the combustion chamber is formed by a housing called the "epitrochoid" that surrounds a triangular rotor. The rotor has three convex faces, each of which functions as a piston, compressing and expanding the combustion chamber as it rotates.
The main advantages of rotary engines are their compact size, smooth operation, and high power-to-weight ratio. They are typically smaller and lighter than conventional engines of the same power output, which makes them suitable for use in small, lightweight vehicles, and aircraft. Rotary engines also have fewer moving parts than conventional engines, which makes them more reliable and easier to maintain.
However, rotary engines also have some disadvantages, such as lower thermal efficiency, higher emissions, and more complex seals, which have been the main reason for their limited use.
Currently, Rotary engines are not widely used in the automotive industry, but they are still used in some area such as aircraft and racing cars. Due to their high power-to-weight ratio and compact size, they could be useful in other applications such as portable generators, drones, and unmanned aerial vehicles.
Control by fuel change refers to the process of adjusting the composition of the fuel used in an internal combustion engine in order to control or optimize its performance. This can include changing the fuel itself or adding additives to the fuel to alter its properties.
There are a variety of ways that fuel can be changed to control an engine's performance, some examples include:
- Changing the octane rating of the fuel, which can affect the engine's compression ratio and the timing of combustion
- Adding oxygenates to the fuel, such as ethanol or methanol, which can increase the engine's power output and reduce emissions
- Injecting water or water-alcohol mixtures into the combustion chamber, which can improve thermal efficiency and reduce emissions
- Using different types of fuel, such as biofuels, hydrogen, or natural gas, which can reduce emissions and decrease the engine's dependence on fossil fuels.
The specific type of fuel changes and the engine's response to them will vary depending on the engine design and the desired outcome. Control by fuel change can be used to improve engine efficiency, reduce emissions, and increase power output. However, using certain fuels or additives can also have negative effects such as increased engine wear, reduction of engine life, or increased emissions of other pollutants.
A catalytic converter is a device that is installed in the exhaust system of an internal combustion engine to reduce emissions. It is designed to convert harmful pollutants, such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into less harmful compounds before they are released into the atmosphere.
Catalytic converters use a catalyst, typically a combination of precious metals such as platinum, palladium, and rhodium, to catalyze chemical reactions that convert the pollutants. The catalytic converter typically has a ceramic or metallic substrate coated with the catalytic material, which provides a large surface area for the reactions to take place.
There are two main types of catalytic converters:
The first one is the Three-Way catalytic converter, which is the most common type used in vehicles. It is able to reduce CO, HC, and NOx simultaneously.
The second one is the Lean NOx catalytic converter, which is used to reduce NOx emissions in lean-burn engines.
Catalytic converters have been mandatory in the majority of vehicles sold in the world since the 1970s. They have been highly effective in reducing emissions of harmful pollutants and have helped to improve air quality in many areas. However, catalytic converters can also be damaged by certain factors such as overheating, improper fuel mixture, or the use of leaded fuels, which can reduce their effectiveness and longevity.
Air pollution by Diesel engines and turbojet engines.
Diesel engines and turbojet engines are both sources of air pollution, although the specific pollutants they emit and the ways in which they emit them can differ.
Diesel engines, which are commonly used in heavy-duty vehicles such as trucks and buses, emit particulate matter (PM), nitrogen oxides (NOx), and other pollutants. Particulate matter, also known as soot, can be inhaled and cause respiratory problems such as asthma and lung cancer. Nitrogen oxides contribute to the formation of smog and acid rain. The emissions from diesel engines can be reduced by using cleaner diesel fuels and by installing catalytic converters and other emission control devices.
Turbojet engines, which are used in aircraft, emit pollutants such as nitrogen oxides, water vapor, and carbon dioxide. Nitrogen oxides contribute to the formation of smog and acid rain. Water vapor can lead to the formation of contrails, which are visible lines of condensed water vapor that can persist in the sky for hours. Carbon dioxide is a greenhouse gas and contributes to global warming. The emissions from turbojet engines can be reduced by using more efficient engines and by developing alternative fuels.
Both diesel and turbojet engines have a significant impact on air quality, and there are ongoing efforts to reduce their emissions. The regulations for both diesel and jet engines have become stricter over the years, and the research and development for cleaner and more efficient engines are ongoing.
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