Modern Internal Combustion Engine

Joab Camarena
December 7, 2015

Submitted as coursework for PH240, Stanford University, Fall 2015


Fig. 1: Four stroke cycle. (Source: Wikimedia Commons)

The internal combustion engine (ICE) is what powers most vehicles today and has been around for many years. The ICE has undergone numerous redesigns solely for the purpose of improving the power output and minimizing energy loses. The way the process works is that there is intake through port openings, which pushes down the piston beginning its cycle of compression and decompression, with the energy from this being transferred to the crankshaft allowing for movement of the vehicle. The more common internal combustion engine relies on four piston strokes to complete its cycle and release energy to move a vehicle. [1-3]

How It Works

There are four steps in this cycle: 1) intake, 2) compression, 3) combustion and power stroke, and finally 4) exhaust (Fig. 1). The process of how this works is as listed:

  1. Intake: A fuel and air mixture enters into the cylinder as the piston shifts down and inlet opens.

  2. Compression: Upon closure of the inlet, the fuel-air mixture increases in pressure and temperature as the piston compresses the gas by moving upward.

  3. Combustion and Powerstroke: Energy is released through a combustion reaction caused by the ignition of a spark plug which combusts the fuel-air mixture and brings it to a high temperature. As the mixture increases in temperature and pressure, it pushes against the piston, hence causing the power stroke, which rotates the crankshaft.

  4. Exhaust: The byproducts formed by the combustion reaction are then released through the exhaust pipe and the cycle repeats once the inlet opens and exhaust valve closes. [2,3]

Energy Analysis

Although this is a commonly used engine in vehicles today, it does not mean that it is the most efficient. Combustion inefficiency measures the portion of energy that is not utilized from fuel. It is found that coolant heat loss and exhaust energy heat loss are the biggest sources of thermal loss, which contributes to the lack of energy turnover. It is constantly stated that the Second Law of Thermodynamics limits all engines from reaching maximum thermal efficiency, yet it does not mean we cannot improve the conversion rate of energy. Constant innovation and redesign of the internal combustion engine have allowed for better energy conversion of fuel. [4]


Knowing how the internal combustion engine works and where its inefficiencies lie, proper technology and design of the internal combustion engine will allow us to better utilize the energy within fuel. Although gas prices have been constantly fluctuating, the most likely trend in the future will be increasing gas prices, which will only make the movement to develop highly gas-efficient cars stronger. It is even possible with the ongoing dialogue about divestment from fossil fuels and effects of climate change, that, alongside our current technology boom, we will no longer rely on or use the internal combustion engine to power vehicles in the future.

© Joab Camarena. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. R. Clarke et al., "Engine Induction System and Method," U.S. Patent 4860709, 29 Aug 89.

[2] D. C. Giancoli, Physics: Principles with Applications, 7th Ed. (Addison-Wesley, 2013), p. 421.

[3] B. Crowe, "Internal Combustion Engine," Physics 240, Stanford University, Fall 2012.

[4] M. Baglione, M. Duty and G. Pannone, "Vehicle System Energy Analysis Methodology and Tool for Determining Vehicle Subsystem Energy Supply and Demand," SAE Technical Paper 2007-01-0398, 16 Apr 07.