When the ignition key is turned against spring pressure past the on position to start, the starting contacts close. This connects the cranking-motor solenoid or magnetic switch to the Battery.

转动点火钥匙，弹簧的压力使“开启”位置变为“启动”位置，起动接触器闭合，使得起动电机线圈或磁性开关与电池接通。

youdao

The device automatically disconnects the ignition when the engine is switched off.

该设备在引擎被关闭时会自动断开点火装置。

《柯林斯英汉双解大词典》

When the appointed time came to blast Yuri Gagarin into orbit, he simply pushed a button that completed the ignition circuit and watched the motors start.

当推送尤里·加加林进入轨道的预定时刻来临之际，他只是简单地按下一个按钮闭合点火电路并看着发动机启动。

youdao

Instead of sparking the ignition when the piston is close to top dead center (when the air is compressed), that spark occurs as the piston is pulling away, when the air pressure is at its most turbulent, creating much faster ignition and more power.

FORBES: How To Get 50 MPG Out Of Your Gasoline Engine

But when she turned off the ignition and turned it on again, and tried the starter with the choke out, the engine fired at once.

NEWYORKER: The Woman of the House

That led to an ignition failure when the key was turned and had the potential to set the system catching fire, according to the Hartford Examiner.

FORBES: After 130,000 in 2010, BMW Recalls Another 569,000 Vehicles