In response to this interest, manufacturers have introduced natural gas engine-powered generator sets that feature “lean-burn” technology. The combustion is considered “lean” when excess air is introduced into the engine along with the fuel.
Lean-burn means pretty much what it says. It is a lean amount of fuel supplied to and burned in an engine's combustion chamber. Normal air-to-fuel ratio is on the order of 15:1 (15 parts air to 1 part fuel). True lean-burn can go as high as 23:1.
Reduces the occurrence of “knocking” or detonation. To prevent either knocking or misfiring, the combustion process must be controlled within a narrow operating window. Charge air temperatures and volume, together with air to fuel ratio, are constantly monitored. The micropro-cessor-based engine controller regulates the fuel flow and air/gas mixture and ignition timing.
Design of Engine
The design of the lean-burn engine incorporates a simple open combustion chamber housed in the piston crown. The shape of the piston crown intro-
duces turbulence in the incoming air/fuel mixture that promotes more complete combustion by thoroughly exposing it to the advancing flame front. The flame
plate of the cylinder head is regular (flat) and the spark plug is centrally located. The air and gas fuel are correctly mixed under the control of the engine management system.
One of the results of this technology is significantly reduced emissions in the exhaust.
Cummins’ new lean-burn gas engine generators have NOx emissions
as low as .85 grams/BHP-hr, and produce low amounts of hydrocarbons (HC), carbon monoxide (CO) and particulate matter (PM). This allows the generator
sets to meet the most stringent air quality regulations without after-treatment devices in the exhaust stream.