5 Gas analysis
Determining Engine Efficiency through Emissions
Examining CO2 levels can provide valuable insights into quickly assessing an engine's combustion efficiency. CO2 levels below 12% suggest incomplete combustion, while readings above 12% indicate efficient combustion, possibly signaling a failing catalytic converter.
Components of Emissions
Hydrocarbons (HC): Raw or unburned gasoline resulting from incomplete combustion. HC combines with NOx and sunlight to form photochemical smog.
Carbon Monoxide (CO): Partially burned fuel, indicating a rich air-fuel mixture. CO is highly toxic and reduces oxygen in the bloodstream.
Oxides of Nitrogen (NOx): NOx is formed at high combustion temperatures (>2500 degrees) when oxygen combines with nitrogen. Along with HC and sunlight, NOx contributes to the formation of ozone or smog.
Carbon Dioxide (CO2): A measure of combustion efficiency, formed during complete combustion. Oxygen combines with HC and CO to produce CO2 and H2O.
Oxygen (O2): Supports combustion and serves as a lean indicator.
Causes of HC Emissions
Various factors can lead to elevated HC emissions:
Electrical misfires: The absence of a spark leads to unburned fuel in the exhaust.
Advanced ignition timing: Premature ignition results in incomplete combustion and increased HC levels.
Lean air-fuel mixtures: Insufficient fuel relative to oxygen leads to incomplete combustion.
Rich running conditions: Excess fuel causes incomplete combustion, raising HC and CO levels.
EGR valve open at idle: Inert exhaust gas at idle increases HC levels.
Low idle speeds: Insufficient airflow reduces combustion efficiency, raising HC emissions. Additional causes include leaking piston rings, burnt valves, and malfunctioning components like air injection systems or catalytic converters.
Causes of CO Emissions
CO emissions stem from incomplete combustion due to rich air-fuel mixtures or other factors like:
Plugged PCV valve: Reduced oxygen supply leads to incomplete combustion and elevated CO levels.
Dirty air filter: Decreased intake manifold vacuum triggers a rich fuel command, increasing CO emissions.
Fuel in crankcase: Unmetered fuel drawn through the PCV system raises CO levels.
Saturated EVAP canister: Continuous uncontrolled vapor and fuel flow into the engine results in a rich mixture.
Other contributors include malfunctioning components like air injection systems, catalytic converters, or computer controls.
Causes of NOx Emissions
High combustion temperatures lead to NOx formation, exacerbated by factors such as:
Advanced timing: Premature ignition increases pressure and temperature, elevating NOx emissions.
EGR valve malfunction: Inadequate exhaust gas recirculation raises combustion temperatures, increasing NOx.
High-performance parts: Enhanced engine efficiency increases combustion temperatures and pressures, boosting NOx production.
Cooling system problems: Inefficient heat dissipation elevates NOx emissions.
Low octane fuel: Lower ignition temperatures cause premature fuel ignition, increasing NOx levels.
Other contributors include lean air-fuel mixtures, carbon build-up, or turbo/superchargers.
Causes of CO2 Emissions
CO2 levels reflect combustion efficiency, and deviations from optimal levels can indicate combustion issues. Factors affecting CO2 levels include incomplete combustion due to misfires or component malfunctions.
Causes of O2 Emissions
O2 emissions indicate unconverted oxygen and can serve as a lean indicator. Causes of high O2 include lean conditions, misfires, air injection problems, or exhaust leaks.
