Fuel, Air and Ignition Systems flashcards

$AFR=\frac{m_{air}}{m_{fuel}}$, a mass ratio written as a number to 1. Divide, never add: 375 g air with 25 g fuel gives 15:1. Gasoline stoichiometric is about 14.7:1.

$\lambda =\frac{AF{R}_{actual}}{AF{R}_{stoich}}$, unitless. $\lambda =1$ is stoichiometric, below 1 is rich (extra fuel), above 1 is lean (extra air). 13.23/14.7 = 0.90, rich.

No. Fuel is in the denominator, so a higher AFR means less fuel per unit of air, a lean mixture. A lower number (such as 12:1 for gasoline) is rich.

Tank (stores), pump (moves and pressurizes), filter (removes debris), rail (holds pressurized fuel at the engine), injector (meters fuel by pulse width into the port or cylinder).

The coil is a transformer: when primary current is switched off, it induces tens of thousands of volts in the secondary. The spark plug delivers that voltage as a spark across its gap in the chamber.

Timing is measured in crank degrees before TDC. A larger BTDC number fires earlier (advanced); a smaller one fires later (retarded). The ECM retards timing when the knock sensor detects knock.

Closed loop: the ECM reads the upstream oxygen sensor and corrects injector pulse width continuously. Open loop: fueling from stored tables without oxygen feedback, as during cold start or wide-open throttle.

A sensor reports a condition (crank position, MAF, MAP, oxygen, knock). The ECM decides. An actuator does physical work on command (injector, ignition coil, throttle motor, fuel pump).