unprotected engine

例句：

1. 1. The new car has a completely unprotected engine.
   这辆新车有一个完全无保护的发动机。
2. 2. The old car's engine was damaged due to lack of maintenance.
   那辆旧车因为缺乏维护而损坏了发动机。
3. 3. Engineers are working on developing a more efficient unprotected engine.
   工程师们正在努力开发一种更高效的无保护发动机。