:: R a c i n g S M :: Study - Engine Firing Order (2-Stroke)

Untitled Document

145905 visitors

4563112 hits

Website online since 02/2006

A passionate subject and of great relevance in the performance and character of a 2-Stroke engine is without a doubt the ignition. In the analysis of the monocylindrical one, some decisions have to be taken, to know:

1. The ideal weight of the set crankshaft + flywheel, for a determined engine character/behaviour.
2. Distribution of that weight between crankshaft and the flywheel.

We know that an higher weight in the set favours the traction, a progressive engine, and mainly engines with bigger piston displacements that operate in low rotation regimes, independently of the linear speed of the piston; this is because it favors the decreases and averages rotations, not favoring the high rpms, conferring of this way, to a less explosive and more usable character to the engine. (Examples: Engines with high stroke, low engine rotations, much torque, round engine horspoewer curve, great accelerations and low-mid top speeds.)

On the other hand, peaky engines, with lower piston displacements and/or with high levels of crankshaft rotation, present greater speed and acceleration with a lesser weight in the set, mainly in high rotation (in this version they will be always with worse low and mid rpms, but with better high rpms - where if it finds the power peak in an peaky engine). In raised regimes of rotation, we can almost affirm that how much less weight, better (F1 case). This little weight brings as disadvantages the following phenomena:

More vibrations from the engine.
Faster accelerations in Neutral gear (due to the lower inertia of the light set) causing more instability to the engine.
Bigger consume of the mobile parts.

Examples: engines with low stroke, bigger rpms, high top speed, great engine horsepower and horsepower curve very radical and peaky.

Basically the principles for the monocylindrical one are these; for multi/pluri cilynder, these principles are remained, but new phenomena appear.

The configuration in Line - "Twin" or "V", normally is related in the first case to 180 in 180 degrees explosions to each crankshaft rotation and the "V" to a separation between explosions of 90º, followed of 270º without explosions. However the first version has potential to a more explosive and peaky character, and the second for a bigger control and traction/presentation of the torque and power.

For who intends maximum power, he will have to opt to the “Twin” configuration, being that for who it intends more torque, traction and control will have to opt to the "V". Another characteristic of the Twin, is that for to be to analyze the 2-Stroke engine, with explosion for cylinder to each rotation of the crankshaft, in necessary moment where a piston initiates the difficult ascent of the BDC for the TDC (mainly thus that the exhaust window for the effect is closed compression), it receives the support proceeding from the explosion in the other cylinder, being of this helped form: the two cylinders are helped mutually, for that it strengthens its TWIN character.

We have therefore a highest number of explosions, that associated to a 2-Stroke explosive character making rotation, will be able to confer a highest power in high regimes.

It makes possible the great magic, the great dream.....but..... what’s the great dream?

It is treated to change the position of the crankshafts in such form, that explosions of 90º in 90º are obtained (SCREAMER System), in contrast of the traditional explosion order in the 500 GP, with 2 simultaneous explosions followed of others 2 in simultaneous passed 180º of crankshaft rotation.
The 2nd version, standard, isn't more than a double Twin, with very identical sound.

The 1st version, for the fact to separate the explosions and to eliminate its concurrence, confers a F1 sound alike to the engine.
Let's see: if a 500 GP engine, with four 125 cylinders cm3 (54*54,5) reving till 13 500 RPM (values of the MotoGP 125/250), we will have 13 500 * 4 explosions when the engine goes in the maximum. This corresponds the 900 explosions for second! Or either, in the Screamer version, with the engine reving in max RPM, we will have inside 1 SECOND, 900 explosions separated ones between itself!

It's equivalent to fraction 1 second into 900 parcels and to know that in each one of them it's an 125 cm3 explosion - That is F1! It creates a supersonic effect!
And... for beyond the incredible sound, which impact it will have in the behavior of the engine? It's peaky, with worse low and mid power, but with incredible top power, in a cocktail of high explosions in regimes incomparable.