double-expansion engine

例句：

1. 1. The double-expansion engine is the heart of our new car's powertrain system.
   双膨胀发动机是我们新汽车动力传动系统的心脏。
2. 2.This engine has a double-expansion design, which significantly improves its efficiency.
   这款发动机采用了双膨胀设计，大大提高了其效率。
3. 3. The double-expansion engine has been proven to be more energy-efficient than traditional engines.
   双膨胀发动机已被证明比传统发动机更加节能。