How to Improve Efficiency of Internal Combustion Engines

The efficiency of internal combustion engines is an important factor for mechanical engineers. Engineers have been devised various methods such as direct fuel injection, VIT, turbo-charging, cam-less engines, and regenerative braking to improve the efficiency of engines. There are several factors that reduce the efficiency of engines. Let us look at the various ways to improve efficiency.

What exactly is the efficiency of an internal combustion engine? There is fuel that is supplied per unit time for carrying out the work. The efficiency is calculated to check if the output of the engine shaft is equivalent to the initial energy supplied after deducting all losses.

The calorific value and mass of the fuel is used to determine the fuel’s input power. A brake dynamometer can be used to measure the shaft output. So, efficiency is nothing but the ratio of output to input. An Internal Combustion Engine on an average has an efficiency ranging between 20% and 30%. This efficiency is very low and has to be improved. An Engineer-in-training or EIT will be able to understand the impact of efficiency of internal combustion engines.

The Internal Combustion Engine’s efficiency can be improved using the below given methods.

Regenerative Braking: Whenever you apply brakes on an automobile like a car, there is a loss of heat and so a loss of kinetic energy. Using regenerative braking you can prevent this loss whenever you apply the brakes while moving in a downward direction. This is a type of electromagnetic braking where small motors absorb the wasted energy and converts that energy into battery power. Taking the PE Exam will help to learn about various energy saving measures.

Variable Injection Timing: Maritime Engines make use of Variable Injection Timing. For maintaining mean effective pressure, the injection is improved when the load is low and speed is also lesser. The engine efficiency improves, because the scavenge pressure is maintained. The quantity of burning fuel may be of a lesser quality. The Fundamentals of Engineering Exam will help you to focus and find ways of improving engine efficiency.

Variable Valve Timing: The opening and closing time of the inlet and exhaust valves can be changed from time to time. This change in the opening and closing times increases the efficiency of the engine by 4% to 5%.

Cutting off Cylinders: While cruising or going downhill, if the engine is large, half of the cylinders can be cut off resulting in reduced fuel demand. But this cutting of cylinders cannot be done on small engines as the engines will become rough, though it is useful for large engines.

Turbochargers: Combustion can be optimized as a turbocharger uses an exhaust gas recovery device that helps to boost up air pressure. The efficiency of the engine is increased by 7% to 8%. The FE Exam Prep Certification guides you in knowing the various ways to improve efficiency of internal combustion engine.

Direct Fuel Injection: In engines, usually the fuel will be injected only after mixing with air. But nowadays the fuel is directly sent to the combustion chamber and the mixing takes place automatically. This automatically mixing of air with fuel increases the engine efficiency by 11 % to 13%. 

Viscosity of Oils: The lubricating oils must have the correct viscosity. If the viscosity of lubricating oils is not proper then there are energy losses due to friction.

The topic of combustion is covered in the Mechanical FE Exam syllabus of NCEES under the heading of Thermodynamics.