How Diesel Fuel Tanks Work: Pressurized Or Not?

The topic of whether diesel fuel tanks are pressurized is an important one, especially for car owners and those interested in fuel systems. Fuel tanks can be categorized into two types: atmospheric tanks and pressurized tanks. Atmospheric tanks are typically used for fluids that can be stored under normal conditions, such as crude oil and water. On the other hand, pressurized tanks are designed for liquids that require stabilization and storage under pressure, such as liquefied petroleum gas (LPG) and liquefied natural gas (LNG).

When it comes to diesel fuel tanks, the answer to whether they are pressurized is not a straightforward yes or no. While some diesel fuel tanks may be pressurized, it is not a universal feature. The need for pressurization depends on various factors, including the type of fuel, the vehicle's make and model, and environmental considerations.

In general, car fuel tanks are pressurized to control emissions by preventing gasoline vapors from being released directly into the atmosphere. This system helps to reduce the escape of fuel vapors, contributing to environmental protection. However, not all vehicles have pressurized fuel tanks; for example, Formula 1 cars do not pressurize their fuel tanks.

It's important to note that the presence or absence of pressurization in diesel fuel tanks can impact engine performance and fuel efficiency. Inconsistent fuel flow and pressure can lead to issues such as fuel starvation or rough idling. Therefore, it is crucial for vehicle owners to understand the design and functioning of their fuel tanks to ensure optimal performance and maintain the safety of their vehicles.

Car fuel tanks are pressurised to prevent gasoline vapours from being released into the atmosphere

The purpose of a fuel pump in a pressurised car fuel tank is to pump fuel from the tank to the engine while maintaining the proper pressure needed for fuel delivery. If the fuel tank is not pressurised, it can lead to inconsistent fuel flow and pressure, resulting in engine performance issues such as fuel starvation or rough idling.

A pressurised car fuel tank is vented through a valve or vent system, allowing air and fuel vapours to escape while maintaining pressure inside the tank. This system helps to reduce the amount of fuel vapours that escape, contributing to environmental protection. The EVAP system in cars is specifically designed to filter fuel vapours and prevent the gas tank from becoming overly pressurised, which could result in hazardous situations, including fires.

The amount of pressure in the gas tank depends on the temperature of the gasoline—the higher the temperature, the more pressure there will be. Gasoline is made up of over 500 different hydrocarbons, which vaporise when running, creating pressure in the tank. This pressure is normal and helps control and capture gasoline vapours, preventing their release into the atmosphere.

To release the pressure from a gas tank, one can carefully push the valve inside the fitting using a rag and a screwdriver. This process should be done with caution to catch any fuel released due to pressurisation.

Diesel fuel tanks are not always pressurised

Atmospheric tanks can have a floating roof that floats on the fluid or a fixed cone roof attached to the tank walls. The floating roof design is chosen to reduce the vapour area above the liquid and minimise the risk of fire. This type of tank does not need to be pressurised as it is open to the atmosphere, allowing the pressure to equalise and preventing a large pressure difference from developing.

However, there may be certain situations where diesel fuel tanks are pressurised. For example, in some aircraft, fuel tanks are pressurised to prevent fuel vapours from escaping into the atmosphere. Additionally, in very high-performance engines, fuel-injection systems may require fuel to be supplied at high pressure.

It is important to note that diesel fuel tanks, whether pressurised or not, should always be handled and maintained by qualified professionals to ensure safety and proper functionality.

Atmospheric tanks are used for fluids that can be stored under ambient conditions

Atmospheric tanks can either be open to the atmosphere or enclosed. They are often cylindrical with a flat bottom at ground level, which is the minimum cost design. Atmospheric tanks require vents to prevent pressure changes caused by temperature changes, or the addition/removal of liquids.

Atmospheric storage tanks are used to store potentially volatile substances like gasoline, crude oil, other hydrocarbons, and hazardous chemical products. They are typically much larger than pressure tanks, with some capable of holding thousands of gallons.

There are two main types of atmospheric storage tank: fixed roof and floating roof. Fixed roof tanks have a cylindrical shell with a welded roof that can be dome-shaped, conical, or flat. Floating roofs float on the fluid surface and rise/fall with changes in liquid level. They are ideal for storing hydrocarbon liquids with a flashpoint below 37.8°C.

Overall, atmospheric tanks are a safe and cost-effective solution for storing fluids under ambient conditions.

Pressurised tanks are used for fluids that need to be stabilised and stored under pressure

Pressurised tanks are designed to store fluids at pressures above atmospheric pressure. They can be spherical or bullet-shaped, and are often used for liquids with high vapour pressure, such as LPG. The pressure in these tanks can vary depending on the fluid being stored and the desired storage conditions.

In the context of car fuel tanks, pressurisation is commonly employed to control emissions by preventing gasoline vapours from being released into the atmosphere. The pressure in the fuel tank helps capture vapours and regulate their release, contributing to environmental protection. However, not all vehicles utilise pressurised fuel tanks, and high pressure in the fuel tank can lead to dangerous conditions if not properly managed.

It is worth noting that diesel fuel tanks may or may not be pressurised, depending on the specific vehicle and its fuel system design. Some diesel vehicles use pressurised tanks to maintain consistent fuel flow and pressure, ensuring optimal engine performance and efficiency. In contrast, other diesel vehicles may employ atmospheric tanks or vented fuel caps to manage the fuel system.

Pressurised tanks are very expensive and cannot be manufactured in large sizes

Pressurized tanks are used for liquids that need to be stabilized and stored under pressure, such as LPG (liquefied petroleum gas), LNG (liquefied natural gas), and liquid nitrogen. They are also used in power plants that utilize a heat transfer fluid with a high vapour pressure.

Pressurized tanks are very expensive, and there are several reasons why. Firstly, the manufacturing process and materials used contribute to the high cost. The tanks are typically made from steel or stainless steel, which provides robustness, strength, and resilience under stress and extreme temperatures. Stainless steel also offers the additional benefits of being easy to sanitize and resistant to corrosion. The selection of materials must consider factors such as overall strength, corrosion resistance, return on investment, and convenience of fabrication and maintenance.

Another factor that makes pressurized tanks expensive is the specialized design and safety criteria they must adhere to. These tanks are designed to store and convey gases, vapors, and fluids at elevated pressures, which poses significant safety risks. Certified experts carefully calculate the design parameters, such as design pressure, maximum allowable working pressure, and design temperature, to ensure the tanks can withstand the required pressure levels without failing. The tanks must also undergo rigorous testing to evaluate their load-bearing capacity and performance under extreme conditions.

Furthermore, pressurized tanks cannot be manufactured in large sizes due to technical limitations and space availability issues. The larger the tank, the thicker the walls need to be to withstand the internal pressure. For very large volumes, special welding technology is required for the thick steel walls, which adds to the cost and complexity of manufacturing. Additionally, large-scale tanks often face challenges related to social acceptance and space availability.

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