High Fuel Consumption ..The Exhaust (1)

So far, we have talked about how cars take in air, its effect on fuel consumption, spark plugs (see earlier posts). Now in this post, we would be dealing with another ignored part of the car that affects fuel consumption a great deal. Just as cars breathe in, they also breathe out. through the car exhaust. The aspect is of great importance as the air that comes out of the car exhaust, if not checked, can be harmful to us humans as we breathe the same air. In order to make sure that the harmful gases are eliminated, the Oxygen Sensor (to check the air/fuel mixture) and the Catalytic Converter (to break down this harmful gases to water (H₂O) & carbon dioxide (CO₂)) are placed along the exhaust pipe. Hence the reason you see droplets of water from the exhaust pipe. Lets start with the oxygen sensor...




Oxygen sensors have been standard equipment on passenger car and light truck engines since 1980-81. Most such vehicles have one or two oxygen sensors (two are typically used on selected V6 and V8 engines starting in the late 1980s). Since the introduction of On-board Diagnostics II (OBD II) in 1995-96, the number of oxygen sensors per vehicle has doubled (the extra sensors are used downstream of the catalytic converter to monitor its operating efficiency. The oxygen sensor monitors the level of oxygen (O₂) in the exhaust so an on-board computer can regulate the air/fuel mixture to reduce emissions. The sensor is mounted in the exhaust manifold downpipe(s) before the catalytic converter or between the exhaust manifold(s) and the catalytic converter(s). It generates a voltage signal proportional to the amount of oxygen in the exhaust. The sensing element on nearly all oxygen sensors in use is a zirconium ceramic bulb coated on both sides with a thin layer of platinum. The outside of the bulb is exposed to the hot exhaust gases, while the inside of the bulb is vented internally through the sensor body or wiring to the outside atmosphere.

When the air/fuel mixture is rich and there is little O₂ in the exhaust, the difference in oxygen levels across the sensing element generates a voltage through the sensor's platinum electrodes: typically 0.8 to 0.9 volts. When the air/fuel mixture is lean and there is more oxygen in the exhaust, the sensor's voltage output drops to 0.1 to 0.3 volts. When the air/fuel mixture is perfectly balanced and combustion is cleanest, the sensor's output voltage is around 0.45 volts. To be continued...