Not 100% relevant, but one spark plug will not succeed in igniting all of the fuel. I know this from aeroplane engines, which are fitted with two magnetos, and two spark plugs per cylinder. Part of the engine checks before each flight involves switching off first one magneto, then the other. You would expect the RPM to drop by between 100 and 150 (from a starting RPM of between 1800 and 2200 depending on the engine - so that's around a 5-8% drop). Any more than that means you've probably got a fouled spark plug. And if there's no drop at all, that means the p-lead which turns the magneto off is probably broken, and you're still running on all 8 plugs. Thus, the fuel is definitely burned more efficiently with 2 sparks than it is with 1.
This doesn't necessarily mean that having 5 sparks from 1 spark plug will improve things. Firstly, each spark in the aeroplane engine is full-strength, switching off a magneto reduces the total spark strength by half as well as reducing the number of sparks, and I don't know what proportion of the RPM/power drop is due to reducing the spark strength and what proportion is due to reducing the number of sparks. Also, the sparks are located at opposite ends of the cylinder - one in the top, one in the bottom (this is in a horizontally-opposed engine), whereas the 5 sparks in the single spark plug would all be at approximately the same place. I have flown planes with magneto switches in very inconvenient locations - and have accidentally turned off one of the magnetos in flight with my left elbow while operating the throttle on a couple of occasions. The difference in power was barely noticeable - there was no immediate difference in performance, but each time, I noticed the plane had lost a little bit of altitude, and discovered the switched off magneto when investigating. Unfortunately, I don't know how long the switch had been in this position before I noticed it, so I can't really put a number on the power loss caused during flight. And I'm certainly not going to deliberately fly with magnetos turned off to investigate! But judging by the fact that I there's no large or immediate difference in cruise performance or RPM, I don't think that an extra spark makes much difference during cruise. So how does this relate to car engines. Well, the cruise performance (i.e. no noticeable difference) relates roughly to motorway driving - moderate levels of power for extended periods. So I'd guess the multi-spark plugs would make no difference on the motorway. The engine checks relate to putting your foot down (aeroplane engines, unlike car engines, require more power to "rev up" to a certain RPM when stationary than they do to cruise at the same RPM - there's a windmill effect on the propeller which reduces the amount of work the engine has to do once you're moving - so 2200RPM when stationary requires a fairly high power setting). As I said above, there's a 5-8% decrease in RPM at this power setting when one magneto is switched off. (This is at about the same RPM as the cruise by the way - normal cruising RPM is about 2200-2300RPM.) So it seems that, in a car, there might be a noticeable difference in acceleration with multiple sparks - notwithstanding the differences between cars and planes in spark power and placement which I mentioned above. But I'd be very surprised if there was any improvement in motorway fuel economy. This seems to be backed up by reports from people who have fitted the plugs and noticed improved performance. No one has yet said anything about fuel economy, but someone was going to measure this in a car with a fuel-flow gauge - any feedback on this yet? Would be interesting, though, if someone felt like fitting an aircraft engine to a car. Then, put regular spark plugs on one magneto (well, you'd probably want to replace the magnetos with alternators for a car - magnetos don't respond well to sudden changes in RPM) and multi-spark plugs on the other. Drive down the road, under various conditions, and switch between one the first and the second alternator, and see if there's any noticeable difference in performance....... (Actually, this wouldn't be very practical - most aeroplane engines red-line at 2700RPM! Are there any car engines out there which have 2 spark plugs per cylinder, where the driver can switch between them while driving???) Complete (well, almost complete) change of subject - someone mentioned the tool for tilting the car on it's side that was demonstrated at the show. I thought that was a superb idea! Not sure if it would actually take sufficiently long to bolt the C-bars to the car to mean it's not really worthwhile for a quick job, but a good idea anyway. But I did feel sorry for the poor guys who had to stand there demonstrating it - two whole days of pressing a button on a power-drill, then reversing the drill and pressing the button again, over and over! Dean ------------------ > Date: Mon, 11 Mar 2002 12:23:46 -0000 > From: Richard Gosling <[EMAIL PROTECTED]> > Subject: RE: Ally Pally Show Review - and too good to be true gadgets x-ma c-creator="4D4F5353" > > Secondly, > how do the 4 sparks after the first one help? If the first one succeeded in > igniting the fuel, the other will not affect anything /// [EMAIL PROTECTED] mailing list /// Send admin requests to [EMAIL PROTECTED] /// or try http://www.team.net/cgi-bin/majorcool /// Send list postings to [EMAIL PROTECTED] /// Edit your replies! If they include this trailer, they will NOT be sent.
