12-Cylinder Firing Order Display
NOTE: You must have Java Plug-in 1.4.2 05 or later installed
on your machine for this applet to function correctly. The Plug-in is a
free download from Sun.com.
1. Select an engine from the pull down menu at the center of the applet canvas.
2. View the characteristics of that particular firing order.
Most people look at tabulated V-12 firing orders with a degree of confusion
and dismay. Not only does it first appear that the 12-cylinder sequence is
random, the nomenclature often obstructs by introducing numbering schemes and
letters such as A, B, L, R, D, G to describe the left and right banks. Also,
manufacturers use different references as to the location of number one
cylinder; it maybe either next to the propeller, or on the anti-propeller end.
Additionally, the engine might be either upright or inverted! In an effort to
make V-12 firing orders comparable, the author uses a naming convention adapted
from the German V-12 manufacturers. Beginning at the propeller, cylinders 1-6
are in the right bank, and 7-12 on the left. This applies whether the engine is
upright or inverted. With this convention it is also necessary to know the
direction of rotation of the crankshaft, either CW or CCW as viewed from the
rear, looking toward the propeller. This resolves the complexity of direct
drive, or geared, and removes confusion caused by the characteristics of
different types of gear systems, such as internal or external spur gears, or
epicyclic. Note that engine data plates typically use a propitiatory
manufacturer nomenclature, as well as describing only the direction of rotation
of the propeller.
Description of the Display
At the left of the canvas is a diagram of the 12-cylinder firing
sequence. The columns of numbers closest to the graphic (labeled "N") represent
the normalized cylinder numbering scheme. The other columns of numbers (labeled
"DP") represent the data plate cylinder numbering scheme.
In the center of the canvas is an isometric view of the crankshaft that
depicts the bank firing sequence of the engine. The small arrow at the front of
the crankshaft indicates the direction of CRANKSHAFT (not propeller) rotation.
Note that in all cases the crankshaft has a 6-throw, 120-degree configuration
with crankpins pairs 1-6, 2-5, and 3-4 in the same plane. The arrows depict the
firing order of a single bank. Other considerations aside, it is desirable for
bank firing sequences to alternate from one end of the block to the other. This
improves breathing and scavenging behavior of the engine. The bank firing
sequence graphic facilitates visualization of intake and exhaust flows.
At the right of the canvas is a diagram that allows visualization of crankpin
loading order. This is an important factor in vibration reduction. A good
example is the Junkers Jumo 213. The three examples (213, 213 with Rechlin
order, and 213E) show how changes in firing order made a reliable engine out of
one that was breaking crankshafts. The problem was too many torque reversals per
cycle. This was cured in the 213E by choosing a firing order that systematically
loaded and then unloaded the crankshaft.
This tool works for any 12-cylinder engine with cylinder pairs connected to
the same crankpin of a 6-throw, 120-degree crankshaft, regardless of bank angle.
Because of this, we have included several opposed and H-configuration engines.
You can also enter a new firing order by filling in the table that appears if
you click on the "Create Custom Firing Order" button. In order for the results
to be meaningful, the firing order you enter must be one that can be achieved by
a 6-throw, 120-degree crankshaft within 720 degrees of crankshaft rotation.
It is our desire to expand the number of engines represented to include many
more 12-cylinder engines, including automotive, traction and marine
applications. Please send the data plate firing order, a description of the
cylinder numbering scheme and direction of crankshaft rotation when viewed from
the anti-propeller or flywheel end to