workout wrote:
New RC from 1988 Official Guide
(The following passage was adapted from a work published in 1978.)
The conventional spark-ignition (Otto) automobile engine has inherent virtues that become more apparent when alternative engines are considered. These virtues include a respectable efficiency (especially under partial load), lightweight, ease of starting, acceptable emissions (with control devices), and a negligible requirement for expen~ive fabrication materials (and hence a low manufacturing cost). Nonetheless, concern about air pollution has focused attention on alternative engines that are potentially more promising with respect to achieving minimal emission levels-the compression-ignition (Diesel) engine, the steam or vapor-cycle (Rankine) engine, the gas turbine (Brayton engine), and the Stirling engine.
The conventional automobile engine is indeed at a disadvantage with respect to exhaust emissions because many pollutants are formed as a consequence of the intermittent combustion process, with its rapid chilling of the combustion products. The engine has been substantially cleaned up but, with one or two exceptions, this task has called for catalytic emission- control devices that tend to degenerate rapidly. All the continuous-combustion engines emit far smaller quantities of pollutants than the spark-ignition engine emits in the absence of emission-control devices; in fact, experimental models of vapor-cycle engines, gas turbines, and Stirling engines have surpassed the most stringent emission requirements yet established. Although the Diesel engine is an intermittent-combustion engine, it has the advantage of operating with excess air, so that Its carbon monoxide emission is negligible. Moreover, hydrocarbons are normally only a small constituent of Diesel exhaust. However, because oxides of nitrogen are formed in hot flames and are retained as a result of rapid chilling, the Diesel engine would not be able to meet stringent oxides-of-nitrogen standards. There are also unsubstantiated suspicions that Diesel-engine exhaust particulates carry carcinogens.
If emission standards were to necessitate the replacement of the Otto engine, the Stirling engine would be the most promising candidate. The part-load efficiency of some experimental Stirling engines (40 percent) is the highest of any of the alternative engines. The engine has the further advantage, shared by steam engines and gas turbines, of being able to operate on almost any fuel. It is very quiet, is the easiest of all alternative engines to start, and operates satisfactorily in freezing temperatures. Since the Stirling engine works on a gas cycle, it has the potential of operating at still higher temperatures and pressures than it does at present, which would make it even more efficient and lighter. Unfortunately, because present experimental models need a substantial amount of metal capable of withstanding high temperatures, they would be expensive to manufacture, but there is hope that alternative ceramic components can be developed.
In conclusion, at present the venerable spark-ignition engine remains largely unsurpassed except with respect to emissions. But if an alternative engine must be developed, automobile makers would be wise to invest in the Stirling.
1. According to the passage, the carcinogenicity of Diesel-engine exhaust particulates is
(A) an insoluble problem
(B) a known fact
(C) a common belief
(D) an unsupported hypothesis
(E) an unacceptable risk
2. The passage suggests that the major disadvantage of the spark-ignition engine would be greatly reduced if which of the following were to occur?
(A) A starter that makes the engine much easier to start is invented.
(B) A method of removing oxides of nitrogen from the engine's exhaust emissions is devised.
(C) An emissions-control device that maintains its effectiveness is designed for the engine.
(D) Materials that make the engine much less expensive to manufacture are developed.
(E) Manufacturing materials that make the engine much lighter in weight are developed
3. According to the passage, the Rankine, Brayton, and Stirling engines are similar in which of the following respects?
I. They are continuous-combustion engines.
II. They can operate on almost any fuel.
III. They meet very strict antipollution standards.
(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II, and III
4. It can be inferred from the passage that the major purpose of developing ceramic parts for the Stirling engine would be to replace some current metal components with parts that are
(A) less expensive
(B) lighter in weight
(C) easier to manufacture
(D) more capable of withstanding freezing temperatures
(E) more capable of withstanding high temperatures
5. The passage implies that which of the following is currently a disadvantage of at least one of the alternative automobile engines?
(A) Rapid degeneration
(B) High manufacturing cost
(C) High cost of fuel
(D) Excessive carbon monoxide emissions
(E) Excessive hydrocarbon emissions
6. The author's attitude towards the potential of the Stirling engine can be best described as
(A) ironic
(B) derogatory
(C) confused
(D) cautiously optimistic
(E) completely neutral
7. It can be inferred from the passage that which of the following events, if it were to occur, would immediately cause the most difficulties for manufacturers of automobiles that have Diesel engines?
(A) Emission requirements for carbon monoxide are made more rigid.
(B) Emission requirements for oxides of nitrogen are made very strict.
(C) A study is undertaken to determine whether Diesel-engine exhaust particulates are carcinogenic.
(D) Researchers find that catalytic emission control devices create a by-product that is harmful to health.
(E) Researchers find that all continuous combustion engines have a serious, previously undiscovered drawback when used as automobile engines.
8. Which of the following best summarizes the author's main point?
(A) Except in the area of oxides-of-nitrogen emissions, the Diesel engine is nonpolluting; of the other alternative engines, the Stirling engine is the most promising.
(B) Except in the area of exhaust emissions, the conventional automobile engine is currently better overall than alternative engines; of these, the Stirling engine most warrants further development.
(C) Although the conventional automobile engine has many advantages, its failure to meet stringent emission standards makes the development of the Stirling engine essential.
(D) Although concern about air pollution has focused attention on the emissions of alternative automobile engines, it has not led to the full development of any of them.
(E) Once automobile makers become fully aware of the advantages offered by the spark- ignition engine, they will realize that even the very efficient Stirling engine is not worth developing.
8 minutes, All correct!
1. According to the passage, the carcinogenicity of Diesel-engine exhaust particulates is[/b]
(D) an unsupported hypothesis-
Correct, refer "There are also unsubstantiated suspicions.."
2. The passage suggests that the major disadvantage of the spark-ignition engine would be greatly reduced if which of the following were to occur?(C) An emissions-control device that maintains its effectiveness is designed for the engine.-
Correct, refer "In conclusion, at present the venerable spark-ignition engine remains largely unsurpassed except with respect to emissions..."
3. According to the passage, the Rankine, Brayton, and Stirling engines are similar in which of the following respects?I. They are continuous-combustion engines.- Correct, refer "All the continuous-combustion engines .."
II. They can operate on almost any fuel.
III. They meet very strict antipollution standards.-Correct, refer " in fact, experimental models of vapor-cycle engines, gas turbines, and Stirling engines have surpassed the most stringent emission requirements yet established.."
(E) I, II, and III-
Correct, this option only has both the choices.
4. It can be inferred from the passage that the major purpose of developing ceramic parts for the Stirling engine would be to replace some current metal components with parts that are(A) less expensive-
Correct, refer "Unfortunately, because present experimental models need a substantial amount of metal capable of withstanding high temperatures, they would be expensive to manufacture, but there is hope that alternative ceramic components can be developed.."
5. The passage implies that which of the following is currently a disadvantage of at least one of the alternative automobile engines?(B) High manufacturing cost- Sterling is an alternative automobile engine and refer this part "Unfortunately, because present experimental models need a substantial amount of metal capable of withstanding high temperatures, they would be expensive to manufacture, but there is hope that alternative ceramic components can be developed.."
6. The author's attitude towards the potential of the Stirling engine can be best described as(D) cautiously optimistic-
Correct, refer "if an alternative engine must be developed, automobile makers would be wise to invest in the Stirling."
7. It can be inferred from the passage that which of the following events, if it were to occur, would immediately cause the most difficulties for manufacturers of automobiles that have Diesel engines?(B) Emission requirements for oxides of nitrogen are made very strict.-
Correct, refer "However, because oxides of nitrogen are formed in hot flames and are retained as a result of rapid chilling, the Diesel engine would not be able to meet stringent oxides-of-nitrogen standards.."
8. Which of the following best summarizes the author's main point?(B) Except in the area of exhaust emissions, the conventional automobile engine is currently better overall than alternative engines; of these, the Stirling engine most warrants further development.-
Correct,. Author says Otto is best overall except in the area of exhaust emissions. However, Sterling looks promising provided the cost of manufacturing is brought down.