5.11.1 Ignition is only permitted by means of a single ignition coil and single spark plug per cylinder. No more than five sparks per cylinder per engine cycle are permitted. The use of plasma, laser or other high frequency ignition techniques is forbidden. Only approved ignition coils may be used and the list of parts approved by the FIA, and the approval procedure, may be found in the Appendix to the Technical Regulations.
5.11.2 Only conventional spark plugs that function by high tension electrical discharge across an exposed gap are permitted. Spark plugs are not subject to the materials restrictions described in Articles 5.16 and 5.17.
Rules say nothing about how many electrodes in each spark plug, nor do they say anything about flame ignition.
The OP asked whether an engine without spark plugs or coils would be legal.
Why would the number of electrodes make any difference if there are no spark plugs?
They're not, not using, spark plugs. It's pretty much impossible to have compression ignition beyond 7k rpm, or at the engine loads the ICE sees.
I did not know that. what problems arise at higher RPMs?
Diesels(or compression ignition engines) have relatively small bores, and long strokes. The longer the stroke the higher the average piston speed, that's why high revving motors have big bores short strokes and big rod ratios greater than 1.5(rod length):1(crank throw). It's easier to have compression ignition with smaller combustion chambers. With wide bores it's more difficult because it's easier to have stratified pockets.
Do RC engines have 87mm bores? Looks like a 20mm bore with super short stroke to me. Average piston speed is probably ~25 m/s at full tilt. Compare the piston speed on an F20C even with a generous 1.8 rod ratio and short 86mm throw piston speed at 8,800rpm is ~ 52 m/s which is really freaking high.
Do RC engines have 87mm bores? Looks like a 20mm bore with super short stroke to me. Average piston speed is probably ~25 m/s at full tilt. Compare the piston speed on an F20C even with a generous 1.8 rod ratio and short 86mm throw piston speed at 8,800rpm is ~ 52 m/s which is really freaking high.
86 mm stroke at 8800 rpm is 25.2 m/s. Mean piston speed is independent of rod length.
Do RC engines have 87mm bores? Looks like a 20mm bore with super short stroke to me. Average piston speed is probably ~25 m/s at full tilt. Compare the piston speed on an F20C even with a generous 1.8 rod ratio and short 86mm throw piston speed at 8,800rpm is ~ 52 m/s which is really freaking high.
86 mm stroke at 8800 rpm is 25.2 m/s. Mean piston speed is independent of rod length.
I know this, but engine speed is directly related to it(ie longer rods, shorter throw, higher dwell times, etc). Also brain fart on the piston speed sorry for that, point is that's still higher than the RC engine.
there is a combustion delay inherent with the usual diesel fuels and engines are designed around this delay
(delay time is the basis of rating such fuels - a relatively long delay gives a high Cetane number and this is good)
but this delay time means combustion can't work fast enough for very high rpm
and diesel combustion has very high peak pressures so the pistons and rods have to be very strong so are very heavy
this weight gives forces proportional to the square of rpm, limiting diesels to lower rpm than spark ignition engine's
it all works out
model engines use totally different fuels with very short delay times (and which need less compression to ignite)
most have heat-assisted CI and would not work without the hot point
have a look at the 2 stroke thread viewtopic.php?f=4&t=10966 the last 3 or 4 pages have some discussion on HCCI.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
Another way of explaining initiating
In a regular SI combustion cycle the start of combustion is
triggered by the spark breakdown which takes place between
the electrodes of the spark plug after the ignition pulse has
been applied. The high voltage is creating a strong electrical
field between the electrodes that is strong enough to generate
a highly conductive thin plasma channel (∅ < 50 μm) after
the breakdown. Free electrons in the electrode gap are
accelerated and collide with gas molecules, ionizing them and
creating further “new” free electrons, which lead to an
exponential increase of electrons like in an avalanching
process. The plasma temperature after the breakdown of up to
60.000 K is cooling down by expansion within a few μs to
values in the following arc phase of less than 10.000 K. In the
final glow discharge phase the temperature of the plasma
drops further down and the spark itself extinguishes with
characteristic voltage oscillations when the feeding energy in
the ignition system is becoming too low.
Due to convection processes of the expanding hot plasma in
the spark channel the neighborhood of the gas/fuel mixture is
heated up, where the first radicals are formed that are
triggering the start of combustion, the so-called flame
initiation. The local mixture composition expressed by the A/
F ratio and the local temperature determine the laminar flame
speed which is governing the flame kernel formation and
flame kernel growth. The turbulence structure controls the
spatial homogeneity of the mixture and temperature in front
of the flame zone and therefore indirectly the rate of the
flame kernel growth. When the flame kernel size reaches a
characteristic size of a few millimeters the macroscopic mean
flow in the combustion chamber and the turbulence intensity
are becoming the dominating variables in the turbulent flame
propagation, which governs the major part of the premixed
combustion phase.
In stratified combustion systems only a part of the entire
combustion chamber volume is occupied by the premixed
charge of varying A/F ratio while the remaining rest consists
of fresh air and residuals. In principle the combustion steps
are the same as for homogeneous combustion described
above but limited to the stratified regime, which is
temporarily and spatially determined by the injection process
itself, the interaction with the combustion chamber and the
overall flow pattern. In the combustion chamber of sprayguided
systems the injector and the spark plug locations are
closely located to each other and the flame initiation is only
possible after combustible mixture has reached the vicinity of
the spark gap. Due to this close timing relation the
geometrical arrangement is essential for a successful and
robust flame initiation and the following flame kernel
development period. The first part of the combustion
(inflammation) consists of the flame initiation and flame
kernel growth, Figure 1. At stratified operation the strong
temporal and spatial gradients of the air-fuel charge caused
by the closely timed injection process are becoming in
addition a major contributor to the cyclic variations in a real
engine environment [6].
<figure 1 here>
The variability of the injection process itself causes the
spatial and temporal variability of the mixture quality and
flow pattern and generally tends to increase the overall cycleto-
cycle variations. The diffusive character of the mixture
plume is introducing an additional strong time dependency. If
the time between injection and combustion is too long
turbulent diffusion processes are increasing the incombustible
mixture zones with a too high A/F ratio and/or a too much
diluted mixture composition. As soon as a flame kernel in a
stratified combustion system has been successfully
established the probability of a misfiring cycle is extremely
low [4]. Partial burn can even be stronger when parts of the
mixture regime can not be reached by the flame front due to
separation and isolation. This can be caused by the injection
process itself (e.g. due to temporarily separated multiple
injections or by the turbulent interaction of the mixture plume
with the in-cylinder flow) or also by flame expansion effects.
Such an unfavorable mixture distribution can also result from
a sub-optimal spray characteristic like a multi-hole injector
with desultory mixture regimes from individual spray plumes
can produce [7].
