问题 问答题 简答题

提高发动机实际工作循环热效率的基本途径是什么?可采取哪些基本措施?

答案

参考答案:

提高实际循环热效率的基本途径是:减小工质传热损失、燃烧损失、换气损失、不完全燃烧损失、工质流动损失、工质泄漏损失。提高工质的绝热指数κ。

可采取的基本措施是:

⑴减小燃烧室面积,缩短后燃期能减小传热损失。

⑵.采用最佳的点火提前角和供油提前角能减小提前燃烧损失或后燃损失。

⑶采用多气门、最佳配气相位和最优的进排气系统能减小换气损失。

⑷加强燃烧室气流运动,改善混合气均匀性,优化混合气浓度能减少不完全燃烧损失。

⑸优化燃烧室结构减少缸内流动损失。

⑹采用合理的配缸间隙,提高各密封面的密封性减少工质泄漏损失。

单项选择题
单项选择题

The Supreme Court will hear arguments about the use of public money for the private schooling of children with special needs. It’s interesting to note what’s not at issue: namely, that when a public school system is unable to provide an appropriate education, it is obligated to pay the costs of private school. Too bad poor children don’t have that unshakable right; if they did, there would be no controversy about the District program that gives vouchers to low-income children to attend private schools.

The case to be heard by the court hinges on whether parents have to enroll a child with special needs in public school before the child can attend private school at public expense. Special-education advocates say students shouldn’t have to waste time before being placed in a setting that best suits their needs, while school boards worry about a ruling that could amount to an unfettered fight to private schooling at public expense. What strikes us about the emotionally charged debate is the acceptance by both sides that sometimes it is appropriate to use public money to pay for a child to go to a private school. So, why all the arguments about the approximately$14 million for a federally funded program that lets 1,700 D. C. students attend private schools instead of failing public schools

To hear critics of the D. C. Opportunity Scholarship Program tell it, the use of public money for private schooling is as unprecedented as it is undesirable. In addition to the billions of dollars spent annually on private school tuitions for students with disabilities, private schools get public money for books, technology and teacher training. As long as the money is seen as benefiting the child, it is considered a proper, even desirable, use of public dollars.

Don’t get us wrong. We’re not arguing for the unilateral right of parents to enroll their sons and daughters in any school they wish with the taxpayers picking up the bill. Abuse of special-education policies has contributed to increased costs that threaten to take needed money from general public education funds. Safeguards are needed. Public schools should be pressed to do a better job for students with disabilities and students without. But there are schools in Washington where statistics show that failure is almost guaranteed. If a school system can’t educate a child—whether because of acute special needs or its own historical failings—why should that child not have options for a " free appropriate public education "

What can be inferred from the arguments at the Supreme Court()

A. Too much public money is put into the private schools for children with special needs

B. Public schools are of very poor education quality

C. People consider it is reasonable to use public money for certain students’ private schooling

D. People find it is amusing arguing about spending public money for private schooling