Alternative Energy Demystified, 2nd edition

Stan Gibilisco

Explanations for Quiz Answers in Chapter 6

1. In a diesel-fueled engine, the fuel/air mixture enters the cylinder, facilitating combustion, when the piston is at or near the top of its vertical motion cycle. In Figure 6-6, that situation occurs when the top of the piston is at or close to point X. The correct choice is A.

2. Nitrogen tetroxide serves as the oxidizer in a liquid-fueled rocket. The oxidizer allows the fuel to burn. Without some form of oxidizer carried along with the fuel itself, a liquid-fueled rocket engine could not operate outside the earth's atmosphere. The correct choice is D.

3. Decades ago, tetraethyl lead in conventional gasoline helped to minimize engine knock, an annoying phenomenon that can occur when increased demand is placed on the engine (as when accelerating or driving up a steep hill). The correct choice is C. Unfortunately, the lead in this additive proved physically harmful to humans, even in trace amounts, and it accumulated in the environment as a result of "leaded gas" combustion. For that reason, governments of most countries banned tetraethyl lead for use as a fuel additive.

4. Kerosene has found application in residential heating (particularly in Japan), as a solvent for cleaning purposes, and as a fuel for small portable stoves such as the ones used by campers. However, kerosene has never been (and never will be) used to extinguish fires in entertainment displays, or in any other situation. The reason is obvious: Kerosene burns easily itself! The correct choice is C.

5. An electrostatic dissipation additive minimizes or prevents the buildup of electrostatic charge (sometimes called "static electricity"). Without some means of dissipating this charge, the "static electric" voltage could rise so high that a sudden discharge would cause a spark, igniting the fuel and possibly causing an uncontrolled fire or explosion. The correct choice is C.

6. In a four-stroke engine, ignition occurs at the top of every other complete piston cycle (or every fourth stroke, because each complete piston cycle comprises two strokes, one upward and one downward). The answer is B.

7. By definition, a substance is volatile (or has high volatility) when it easily changes from the liquid state to the vapor state. The answer is A.

8. Petroleum diesel fuel has greater energy density (available Btus per unit volume) than gasoline does, so choice A is wrong. Petroleum diesel fuel has greater physical density (mass per unit volume) than gasoline does, so choice B is wrong. Petroleum diesel fuel contains more sulfur than gasoline does, so choice C is also wrong. However, petroleum diesel fuel can, and occasionally does, crystallize at the extremely cold winter temperatures encountered in some regions. The correct choice is D.

9. Once a solid-fueled rocket engine starts burning, the combustion process can't be stopped until all the fuel has been consumed. This limitation makes solid fuel impractical for use in long-distance space travel where controlled burns are required for navigation purposes. The correct choice is B.

10. The combustion of conventional jet fuel produces carbon dioxide (CO2), a known greenhouse gas. Jet fuel can contribute to the generation of acid precipitation because some forms of it contain sulfur, which reacts in the atmosphere to produce sulfuric acid. Jet aircraft engines occasionally produce contrails, also called "vapor trails," in the upper atmosphere. All three choices A, B, and C represent valid responses, so the answer is D, "All of the above."