The key difference between lean and rich fuel mixture is that we use a lean mixture for maximum efficiency while we use a rich mixture for maximum power in an engine.
We use the terms lean and rich fuel mixtures to describe combustion processes in engines and industrial furnaces. Before analyzing the difference between lean and rich fuel mixture, it is important to know more about the air-fuel ratio. The air-fuel ratio is a parameter regarding internal combustion engines and industrial furnaces. Thus, this ratio is very important for the determination of the efficiency of the engine or furnace. There are three main types of air-fuel mixtures as “lean fuel mixtures”, “stoichiometric fuel mixtures” and “rich fuel mixtures”. Stoichiometric fuel mixture is an air-fuel mixture that contains the exact amount of air required to burn all the fuel in the mixture. Meanwhile, lean fuel mixture has more air than the required quantity of air for the complete combustion of the fuel while rich fuel mixture has less air than the required quantity of air for the complete combustion of the fuel.
CONTENTS
1. Overview and Key Difference
2. What is a Lean Fuel Mixture
3. What is a Rich Fuel Mixture
4. Side by Side Comparison – Lean vs Rich Fuel Mixture in Tabular Form
5. Summary
What is a Lean Fuel Mixture?
Lean fuel mixture is a type of air-fuel mixture that has more air than the required quantity of air for the complete combustion of the fuel. Therefore, this mixture has excess air. These air-fuel mixtures are more efficient but can result in higher temperatures. These temperatures lead to the formation of nitrogen oxides.
Figure 1: Comparison of Rich and Lean Mixture in Diagrams
However, some engines are specifically designed for this type of air-fuel mixtures in order to get higher efficiency. We can call the combustion process in these engines as “lean burn”.
What is Rich Fuel Mixture?
Rich fuel mixture is a type of air-fuel mixture that has less air than the required quantity of air for the complete combustion of the fuel. These air-fuel mixtures are less efficient. It is because these mixtures lack the air required for the complete combustion of the fuel.
Figure 2: Comparison of Power Production by Lean and Rich Fuel Mixtures
However, a rich fuel mixture can produce a very high quantity of energy. The combustion takes place at lower temperatures; thus, we say it burns cooler.
What is the Difference Between Lean and Rich Fuel Mixture?
Lean fuel mixture is a type of air-fuel mixture that has more air than the required quantity of air for the complete combustion of the fuel. Rich fuel mixture, on the other hand, is a type of air-fuel mixture that has less air than the required quantity of air for the complete combustion of the fuel. So, this is the fundamental difference between lean and rich fuel mixture.
Furthermore, a significant difference between lean and rich fuel mixture is that the combustion of the engines using lean fuel mixture occurs at very high temperature while the combustion occurs at low temperatures in rich fuel mixtures. Similarly, lean fuel mixtures produce hotter combustion gases compared to rich fuel mixtures. Moreover, a further difference between lean and rich fuel mixture is that the lean fuel mixtures produce nitrogen oxides whereas rich fuel mixtures produce carbon monoxide.
Above all, the key difference between lean and rich fuel mixture is that we use a lean mixture for maximum efficiency while we use a rich mixture for maximum power in an engine.
Summary – Lean vs Rich Fuel Mixture
The terms “lean” and “rich” in fuel mixtures refer to the air-fuel mixtures with high or lower amounts of air compared to the fuel. However, the key difference between lean and rich fuel mixture is that we use a lean mixture for maximum efficiency while we use a rich mixture for maximum power in an engine. These air-fuel mixtures are useful in internal combustion engines and industrial furnaces.
Reference:
1. James G. Speight Ph.D., DSc, in Handbook of Industrial Hydrocarbon Processes, 2011.
Image Courtesy:
1. “Dosages- pauvres-stoechio-riches” By Biologique – Own work (CC BY-SA 4.0) via Commons Wikimedia