Chemcases: Auto fuels

William Kovarik, Radford University
and Matthew E. Hermes, Kennesaw State University    

(For other award-winning, NSF-funded Chemcases units on food, drugs and environmental chemistry, see this Internet Archive page).


This unit links the physical and chemical properties of gases and liquids, thermochemistry and thermodynamics to the controversial decisions made in the early years of the automotive age. 

Learning goals

  • You will learn about the early development of autos and their fuel.
  • You will understand the decisions based on chemical principles that engineers made to develop autos and fuels that were compatible.
  • Analysis of alternate strategies resulted in invention of tetraethyllead and the decisions to use it in spite of toxicity.
  • What would you have done if you were General Motors or DuPont or Standard Oil in the 1920’s? Would you have introduced tetraethyllead as a gasoline additive?


1. The Need for Light
2. The Need for Transport
3. Variety of Early Fuels
4. Automobiles
5. High Compression Engine
6. Supplying Gasoline from Oil
7. Poor Gasoline Quality
8. Fear of Limited Fuel Supply
10. Knocking
11. Alcohol Fuel as a Replacement
12. Additives/TEL
a. Fuel Thermochemistry
b. Octane and Cracking
c. Fuel Thermodynamics
Case Study


A. The Chemistry and Thermodynamics of Fuels and the Decisions that Led to Worldwide Environmental Exposure to Toxic Lead (TEL) Compounds
The Facts: The invention and development of the automobile as primary mode of personal transportation required a parallel development of the fuels that would power the automobiles. Hydrocarbon fuels were an integral component of society in the 19th century as a source of light. Coal gas, camphene, kerosene from the petroleum in the ground all competed to light the lamps of the cities and the country.

Henry Ford in the First Model T

Automobile engines demanded unprecedented amounts of petroleum. The early refiners could convert only a small proportion of their crude oil to gasoline – the rest was wasted or spilled to the environment. As the number of automobiles increased, two forces played out:a. A shortage of quality fuel that led 1920’s auto industry leaders to predict there would be no more petroleum by about 1940, andb. A requirement for higher quality in the fuels to prevent damaging knocking that robbed the engines of efficiency and power as engineers sought to design high compression auto engines..

1930’s image of combustion pattern

The Chemistry: Automotive fuels derived from petroleum propel our cars by converting the energy of combustion to heat and work. The challenge for an efficient, powerful engine is to maximize the work available. The second law of thermodynamics teaches this can be done by making engines with a high compression ratio. But problems of uneven fuel combustion and knocking must be overcome through fuel reformulation or by finding an appropriate additive.

The History: Automotive designers and engineers had three choices for reformulating and improving fuels.

First: They might provide for a future, non petroleum alternative based on farm-produced ethanol. It turned out that ethanol also had the property of eliminating the knocking problem. They might add significant amounts of ethanol to gasoline initially to prevent knocking and improve the gasoline, anticipating an all ethanol future as petroleum supplies diminished. (Early researchers probaly did not deal with the issues of whether production of ethanol actually consumed more fuel than it produced. This controversy is a current scientific and political issue as we write in the year 20001.)

Second: They might seek better ways of processing crude oil to increase the fraction of the crude that had the properties required for a motor fuel.

Third: They might seek a low concentration additive for gasoline that would improve fuel quality directly. This research direction led to the discovery and implementation of tetraethyllead as an efficient, low concentration gasoline additive that eliminated the knocking.

Tetraethyllead (TEL)

The Questions: How did research along three parallel pathways lead to a number of solutions to the problem of poor quality and insufficient quantity of gasoline.

Students will go through a series of units outlined in the concept map and end with a case discussion on how they would have dealt with the issues of gasoline quality and supply automakers, oil companies and the government faced in the early 20th century.

Begin with the unit on the Need for Light or click on any area of the concept map below.