Diesel combustion has a much greater abundance of air than actually required for stoichometric combustion. But unlike a spark ignited engine (LP, gasoline) a diesel can't run at a stoichiometric condition because you aren't able to get the injected fuel as uniformly distributed. Consequently unless it is a pulling tractor which typically has fire and thick black smoke coming out the stack to get maximum power, you require excess air. At high diesel combustion temperatures much of this excess air becomes NOXs. Lowering the peak cylinder pressure significantly reduces combustion temperatures and thereore NOX, but fuel economy suffers. Two major methods to accomplish this are to retard injection timing, and introduce cooled EGR. Problem is both increase fuel consumption and particulates/smoke. So as NOX goals are lowered, manufacturers have had to add after treatment including a particulate trap to get rid of the smoke/particulates. Alternative is to use urea as an after treatment to change the NOX back to N2 and O, and then tune the engine for more economy by eliminating EGR and using a more optimum injection timing. The "created" O is used to help lower smoke/particulates, making the whole system less complex. Somewhat over simplified the complex issue but should convey the message.
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Today's Featured Article - Engine Valves - Some Helpful Information - by Staff. Intake - On the intake stroke the piston moves doward, sucking in carburized fuel through the open intake valve. Exhaust valve is closed. Compression - With both the intake and exhaust valves closed, the pistons upward stroke compresses or squeezes the fuel into the combustion chamber. Firing - Ignited by the spark, the compressed fuel explodes and forces the piston downward on its power stroke. Intake and exhaust valves are closed. Exhaust valves and seats are exp
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