Pertronics Igniter Conversion
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Air pumps were installed on various engines for various reasons. I'm sure CougarJohn and Ultraranger can add to my post and I welcome it. Some were for dilution as you mentioned. Some were to add oxygen back in to the exhaust to continue the burn. And some were to cool the exhaust valves because of the carb's lean mixture.
Cargo Master
Joined: Sep 2012
Posts: 3,061
Likes: 39
From: Laramie, WY
Advancing the timing gives the air/fuel mixture more time to burn, that raises the combustion temperature and that increases the amount of NOx (Nitric Oxides) created. The amount of NOx created is equal to the amount of time the combustion spends over 1450 degrees.
Retarding the timing decreases the amount of NOx created but creates more CO. Carbon Monoxide comes from incomplete combustion.
The ideal place to set the timing is so that the peak firing pressure is at about 16 to 18 degrees after top dead center. I can measure this on the large bore (18" bore) pipeline engines I deal with. They have a small port into the combustion chamber that I can hook up a pressure sensor to. I then record the pressure in relation to the crank angle. Here's one from a two stroke, a four stroke looks the same it just takes 720 degrees.
Cargo Master
Joined: Sep 2012
Posts: 3,061
Likes: 39
From: Laramie, WY
Catchy little phrase there Ted. I like it.
Air pumps were installed on various engines for various reasons. I'm sure CougarJohn and Ultraranger can add to my post and I welcome it. Some were for dilution as you mentioned. Some were to add oxygen back in to the exhaust to continue the burn. And some were to cool the exhaust valves because of the carb's lean mixture.
Air pumps were installed on various engines for various reasons. I'm sure CougarJohn and Ultraranger can add to my post and I welcome it. Some were for dilution as you mentioned. Some were to add oxygen back in to the exhaust to continue the burn. And some were to cool the exhaust valves because of the carb's lean mixture.
Yes, the air pumps just diluted the exhaust. The exhaust is only hot enough to continue burning for a very short time after leaving the cylinder. And that is only during high power output. When the engine is putting out nearly full power I've measured up to 1700 degrees at the exhaust port on automotive engines. During that time a bit more oxygen could help combust the HC coming out. Otherwise the oxygen is just diluting the exhaust.
Dilution is the answer to pollution...some times the engines I deal with just get mandated to have a taller exhaust stack. That helps dilute the pollution. When you drive by a very tall exhaust stack you can figure it's putting out al lot of pollution.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Back in the day here in Kalifornia you had to have a "smog kit" installed on older cars to pass smog. The "kit" consisted of a yellow sticker in the radiator support, a windshield sticker showing compliance, and last but not least. They would retard the ignition timing to reduce smog.
I never noticed the smog reduction, just the hotter running engine
I never noticed the smog reduction, just the hotter running engine
Orich
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