Problem 74 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is not used as fuel in rocket propellants? (a) liquid oxygen (b) liquid hydrogen (c) liquid hydrazine (d) kerosene oil

Step-by-Step Solution

Answer

Liquid oxygen is not used as a fuel; it's an oxidizer.

Step 1: Analyze Each Fuel Option

Each option given is a potential fuel for rocket propellants. Let's analyze them: Liquid oxygen (O_2) is not a fuel but an oxidizer commonly used in conjunction with hydrogen or kerosene. Liquid hydrogen (H_2) is a common rocket fuel due to its high energy density. Liquid hydrazine (N_2H_4) is used as a monopropellant or fuel in rocket engines. Kerosene oil, commonly used as a rocket fuel, is typically in the form of RP-1.

Step 2: Identify Non-Fuel Components

Among the listed options, analyze which is explicitly not a fuel. Liquid oxygen (O_2) is an oxidizer, meaning it is used to burn the fuel in the combustion chamber but is not a fuel itself. The other options — hydrogen, hydrazine, and kerosene — all actively act as fuels.

Step 3: Determine Correct Answer Based on Analysis

Since liquid oxygen (O_2) is used as an oxidizer and not as a fuel, it is the correct answer. Options (b), (c), and (d) are used as fuels in various propellant combinations.

Key Concepts

Oxidizers

In the world of rocket propulsion, oxidizers play an essential role in helping rocket fuels burn efficiently. Without an oxidizer, the fuels would not combust in the near-vacuum of space where there is no atmospheric oxygen. The oxidizer, such as liquid oxygen (O_2), provides the necessary oxygen molecules to enable the chemical reaction required for combustion.

Key characteristics of oxidizers include:

• They are substances that chemically react with fuels to produce energy.
• They can be solid or liquid, but liquid forms like liquid oxygen are most commonly used in rockets.
• They do not burn on their own, but are crucial to sustain the combustion of the fuel.

Oxidizers are paired with fuels to create a propellant system that is far more powerful than either component could be individually. When combined with fuels like liquid hydrogen or kerosene, oxidizers help achieve the thrust needed to propel rockets out of Earth's atmosphere.

Rocket Fuels

Rocket fuels are substances that generate energy and propulsion when ignited in the presence of an oxidizer. They are the backbone of rocket propulsion systems and can come in various forms, including liquid, solid, and hybrid states. Liquid hydrogen (H_2) and kerosene are examples of rocket fuels commonly used in space exploration.

Two key types of rocket fuel include:

• Liquid Rocket Fuels: Liquid hydrogen is notable for its high efficiency and power, often used alongside liquid oxygen as the oxidizer. It is particularly valued in upper-stage rockets where performance efficiency is critical.
• Solid Rocket Fuels: These are pre-mixed fuel and oxidizer combinations that are simpler to store and handle. However, once ignited, they cannot be easily controlled or stopped until the fuel is exhausted.

In the quest for high efficiency and energy output, engineers continuously research and develop different combinations of fuels and oxidizers to push the boundaries of rocket technology.

Monopropellant

Monopropellants are unique propellant types used in rocketry that consist of a single chemical, which decomposes to release energy. Unlike traditional rockets that require both fuel and oxidizer, monopropellants are self-contained systems. Liquid hydrazine (N_2H_4) is a common example used in satellite thrusters and small maneuvering jets.

The benefits of monopropellants include:

• They allow for simpler engine designs because only one chemical component is required.
• They often require fewer ignition components since the substance decomposes itself—often catalyzed by a heated surface or catalyst bed.
• Because of their simplicity, they are ideal for missions where reliability and ease of use are paramount.

Though not as energy-dense as some bipropellant systems, monopropellants deliver consistent and reliable performance in various aerospace applications.