# Modern engine innovations **URL:** \ **Category:** Factual Questions\ **Created:** [March 7, 2023, 7:21am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823 "2023-03-07T07:21:07Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [March 26, 2023, 6:59pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/41 "2023-03-26T18:59:55Z")
> [@Stranger\_On\_A\_Train](#): > > There doesn’t seem to have been any business activity since 2015, and the founder (Jim Lemke), while a legitimate scientist and inventor, died in 2019. I wouldn’t be holding out much hope that Achates Power is going to produce the next revolution in combustion engine technology any time soon. > [@Ruken](#): > > I’ll meet with someone who used to work there later this month and will ask if it’s still active. Apparently they’re doing some demos for large military vehicles. They still have hopes and dreams for trucks but it’s hard to break into that and many are pushing to skip over new engines directly to BEV or FCEV. ---
**Author:** ![jjakucyk](https://avatars.discourse-cdn.com/v4/letter/j/3d9bf3/32.png) [@jjakucyk](https://boards.straightdope.com/u/jjakucyk)\ **Post date:** [March 27, 2023, 9:24pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/42 "2023-03-27T21:24:52Z")
> [@LSLGuy](#): > > Essential gravy Nice. I’m going to file that away for future use. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [March 31, 2023, 4:48am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/43 "2023-03-31T04:48:08Z")
I was thinking today about my time as a private pilot about 30 years ago. The engines on light planes have two completely separate ignition systems; two magnetos, two distributors, two sets of plug wires, and two spark plugs in each cylinder. If either system has a failure, the engine can run just fine on the other one. It runs a little bit better when both ignition systems are working. In fact, one of the steps on the pre-takeoff checklist is to make sure that both systems are functioning. Set the brakes and run the engine to 2,000 rpm; then turn off one of the magnetos and the revs should drop by about 50. Turn that magneto back on and turn the other one off, and you get the same rpm drop. Turn that magneto back on and the revs should return to 2,000. From what I was told at the time, having two sparks to ignite the mixture in the cylinder results in faster, or more complete burning of the fuel-air mixture, and a little bit more power than just one spark. Why did this never catch on with automobile engines? Sure, it would add some cost and complexity, but compared to other innovations, like variable valve timing, a few extra spark plugs doesn’t seem like a deal breaker. Is there something about car engines (liquid-cooled, multi-valve, swirling fuel-air mix in the combustion chamber) that obviates the benefits of multiple sparks per cylinder? Or maybe this was tried and I just don’t know about it. ---
**Author:** ![Dead\_Cat](https://avatars.discourse-cdn.com/v4/letter/d/9fc29f/32.png) [@Dead\_Cat](https://boards.straightdope.com/u/Dead_Cat)\ **Post date:** [March 31, 2023, 6:14am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/44 "2023-03-31T06:14:30Z")
Here’s one that I happened to recall, there were likely others: > **[Alfa Romeo Twin Spark engine](https://en.wikipedia.org/wiki/Alfa_Romeo_Twin_Spark_engine)** > > Alfa Romeo Twin Spark (TS) technology was used for the first time in the Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars (GTA, TZ) to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls. > In the current Alfa Romeo world the "Twin Spark" name usually refers to the dual ignition engine... ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [March 31, 2023, 6:59am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/45 "2023-03-31T06:59:07Z")
> [@Robot\_Arm](#): > > Is there something about car engines (liquid-cooled, multi-valve, swirling fuel-air mix in the combustion chamber) that obviates the benefits of multiple sparks per cylinder? I suspect that the reason you lose RPM when you switch off one of the ignition systems is that the cylinders on those engines is optimized to have two separate sparks, with two separate flame fronts propagating through the cylinder and optimally meeting in the middle. With a car engine, since the redundancy isn’t anywhere near as critical, the placement of the spark and the resulting flame front can be optimized for a single spark system. That was the entire point of the hemi engine, a hemispherical cylinder head to optimize fuel burn. Modern car engines pay a lot of attention to fluid dynamics to optimize fuel in and exhaust out, and also optimize how the flame front propagates through the cylinder to get the maximum efficiency out of the fuel burn. This is admittedly just a guess, but I suspect that if you compare the overall efficiency of the plane engine with its dual sparks to a car’s single spark efficiency, they would probably work out to be about the same. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 31, 2023, 7:17am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/46 "2023-03-31T07:17:58Z")
> [@Robot\_Arm](#): > > Why did this never catch on with automobile engines? Sure, it would add some cost and complexity, but compared to other innovations, like variable valve timing, a few extra spark plugs doesn’t seem like a deal breaker. Is there something about car engines (liquid-cooled, multi-valve, swirling fuel-air mix in the combustion chamber) that obviates the benefits of multiple sparks per cylinder? Or maybe this was tried and I just don’t know about it. With two intake-ports, two intake valves, two exhaust ports and two exhaust valves, The cylinder head can get kind of crowded, making it difficult to find a place to install a second spark plug. It’s been done on a few automotive engines here and there, but generally only when you have larger cylinders. BMW has been doing it for many years on their boxer twin engine. These engines are typically around 1200 cc’s, so 600 cc’s per cylinder, leaving a bit more room to put second spark plug off to one side in addition to one centrally located spark plug. Large bore engines are also the ones in which you would see the most gain from having two spark plugs per cylinder because the larger bore generally takes longer for its burn to finish. If you have small cylinder bores, the burn already finishes pretty quickly with just one spark plug, so adding a second spark plug doesn’t confer very much benefit in terms of efficiency. ---
**Author:** ![kferr](https://avatars.discourse-cdn.com/v4/letter/k/71e660/32.png) [@kferr](https://boards.straightdope.com/u/kferr)\ **Post date:** [March 31, 2023, 8:58am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/47 "2023-03-31T08:58:44Z")
> [@Francis\_Vaughan](#): > > No doubt Ferrari had a word in the FIA’s ear as well. FIA = Ferrari International Assistance ---
**Author:** ![KMS94](https://avatars.discourse-cdn.com/v4/letter/k/ad7895/32.png) [@KMS94](https://boards.straightdope.com/u/KMS94)\ **Post date:** [March 31, 2023, 3:27pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/48 "2023-03-31T15:27:25Z")
> [@Robot\_Arm](#): > > Or maybe this was tried and I just don’t know about it. My 2013 Dodge Durango with the 5.7 liter hemi has two plugs per cylinder. Some Harley-Davidsons do too. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [March 31, 2023, 4:55pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/49 "2023-03-31T16:55:31Z")
> [@engineer\_comp\_geek](#): > > With a car engine, since the redundancy isn’t anywhere near as critical, the placement of the spark and the resulting flame front can be optimized for a single spark system. That was the entire point of the hemi engine, a hemispherical cylinder head to optimize fuel burn. Modern car engines pay a lot of attention to fluid dynamics to optimize fuel in and exhaust out, and also optimize how the flame front propagates through the cylinder to get the maximum efficiency out of the fuel burn. All well and good, but if they designed an engine with two spark plugs, they could optimize it for two flame fronts, etc. Not that it would be easy, and maybe it’s not worth the effort for the amount of performance that’s gained (or there are easier/cheaper ways to get the same improvement). > [@KMS94](#): > > My 2013 Dodge Durango with the 5.7 liter hemi has two plugs per cylinder. Some Harley-Davidsons do too. So it can be done. ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [March 31, 2023, 5:02pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/50 "2023-03-31T17:02:30Z")
I think **Machine Elf** is right in that it probably has to do with available space in the cylinder head. I don’t know my aircraft engines, but the Lycoming O-320 is a 5.4L 4-cylinder. Those are some big-ol’ cylinders. It also loafs along at 2700rpm. (Correct me if I found the wrong specs). Automotive engineers need to keep car engines small (for efficiency) but then need to rev them high to actually make power. In order to breath under those circumstances, cylinder head space is probably best spent on making the valves as large as possible. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [March 31, 2023, 5:45pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/51 "2023-03-31T17:45:34Z")
Visual aid on a similar but different elephant. > **[1971 Plymouth Hemi Cuda Pro Stock Sox & Martin, 426 CI, 4-Speed | Mecum...](https://www.pinterest.com/pin/318559373632830093/)** > > Jan 17, 2016 - Auction Lot S150.1, Kissimmee, FL 2011. Quarter Mile Legends. Extensive restoration to its '71 race configuration and is in exquisite condition. 426 CI Hemi engine with dual plug cylinder heads, dual quad intake. 4-speed transmission... ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [March 31, 2023, 8:36pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/52 "2023-03-31T20:36:06Z")
Electronic ignitions can produce multiple sparks from a single plug that are just as effective as using two plugs. The redundancy is not needed in cars because of their low cruising altitude. Some planes use multi-spark ignition on multiple plugs, but adoption of new ignition technology on planes can be slow because technology proven reliable over time is preferred. At some point the extra space used in the head makes multiple plugs less effective no matter how many sparks are produced. I don’t know exactly what was done, but designs for electronic car ignitions using multiple sparks of variable length dynamically adjusted for actual performance were proposed. ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [April 8, 2023, 11:41pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/53 "2023-04-08T23:41:04Z")
Can you say more about multiple sparks from a single plug and/or provide a reference? My initial thought was that a second spark from the same place wouldn’t have any fuel to burn, but then it occurred to me that you could play with the swirl and flame front to have fresh fuel/air at the plug in time for the second spark. Is that how this works? And can you name a production car or two that implements this? I’m acutely curious. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 9, 2023, 12:05am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/54 "2023-04-09T00:05:21Z")
> [@steronz](#): > > I don’t know my aircraft engines, but the Lycoming O-320 is a 5.4L 4-cylinder. Those are some big-ol’ cylinders. It’s also just two valves per cylinder, leaving plenty of space for secondary spark plugs. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 9, 2023, 12:53am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/55 "2023-04-09T00:53:58Z")
Back in the late 1970s / early 80s I was in the car hop-up biz. This stuff was the hot set-up for ignitions and we put them in most of our project cars. > **[Ignition Boxes - Holley](https://www.holley.com/brands/msd/products/ignition/ignition_boxes/)** > > Digital performance at an analog price The brand name MSD stands for “Multiple Spark Discharge” which was their innovation and their secret sauce. They did not belong to Holley then, but there’s been a lot of consolidation in performance automotive in 40 (Yipes!) years. I haven’t reviewed the website in detail, but you may learn something from the vids or pages. The difference in light-off with one of their ignition systems versus box stock 1980s GM or Ford coil-in-distributor systems was astonishing. It was a drop-in in the sense that the rest of the induction & fuel system were not redesigned to take advantage of the multiple sparks. I have to imagine that any current cars using MSD techniques from the factory have had those things optimized as a complete system, not a backyard hodgepodge. ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [April 9, 2023, 1:25am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/56 "2023-04-09T01:25:05Z")
Awesome. Thank you, LSLGuy. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [April 9, 2023, 1:47am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/57 "2023-04-09T01:47:58Z")
Hell, Saab measured the electrical resistance of each spark plug when the plug wasn’t firing, in an effort to improve… something. All I know, as the owner of three Saabs, is that those DIC modules are not cheap. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 9, 2023, 3:51am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/58 "2023-04-09T03:51:46Z")
> [@EdelweissPirate](#): > > My initial thought was that a second spark from the same place wouldn’t have any fuel to burn, but then it occurred to me that you could play with the swirl and flame front to have fresh fuel/air at the plug in time for the second spark. The disadvantage of this method ( compared to having two independent spark plugs separated by a useful distance) is that you need to wait, after the first spark, for unburned mixture to be convected into the spark gap. Not just that, but you need to wait long enough for the new ignition event to be positioned meaningfully far from where the initial ignition event has been convicted t to. With two spark plugs, there’s no delay: you can fire them both simultaneously. > [@Crafter\_Man](#): > > Hell, Saab measured the electrical resistance of each spark plug when the plug wasn’t firing, in an effort to improve… something. The chemical reactions of the combustion event temporarily produce ions within the flame front, resulting in lowered electrical resistance. If you bias the spark gap with a DC voltage, then when the flame front goes by, the ion activity results and an electrical current flow across the spark gap. Best guess is that it was some kind of diagnostic that was checking to make sure the mixture was actually lighting off when the spark plug fired, or maybe even checking to see if the combustion had been properly completed (by checking to see when the flame front finished traveling around the combustion chamber and returned back to the spark gap). ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [April 9, 2023, 5:07am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/59 "2023-04-09T05:07:04Z")
As far as twin-engine aircrraft, especially the large jets - what’s the logic of putting the engines so far apart? It would seem to me that the spacing we see on small bizjets where the engines are hung off the rear barely clearing the fuselage is optimum placement to minimize asymettric thrust. zis it noie, vibration, the better to generate lift. Obviously the wing spar needs to accomodate the engine weight and so the longer the spar out to the engine, the more weight. Will going turbo-electric mitigate this design issue (less noise/vibration)? ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [April 9, 2023, 8:03am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/60 "2023-04-09T08:03:26Z")
> [@md-2000](#): > > especially the large jets - what’s the logic of putting the engines so far apart? On large flexible swept wings there is an issue where the wings twist, which can lead to uncorrectable stability issues, (this an exacerbated version of Dutch Roll, where dynamic wing twisting acts to make the yaw induced instability even worse) eventually leading to the aircraft executing an uncontrolled roll. A key innovation in controlling this was to place a controlling mass on the flexible wing. (The other being the dynamic yaw stabiliser, which helps tame Dutch Roll of any cause.) This controlling mass moment takes the form of the mass of an engine on the end of its pylon. So the engine needs to be placed out along the wing structure in a position where it usefully controls the wing twist, and out on a pylon to get enough moment. The pylon helps with logistics of balance and other useful attributes, so it is an overall win. On smaller planes (where small is say 737 or smaller) the wings are stiff enough that this isn’t so much of an issue. 747, 777, 787 etc the wings need this stabilising. They could be built stiff, but at a significant weight penalty, or they could be straight. Swept places them behind the cone of disturbed air from the nose, which is a significant win, and part of how the fuel efficiencies were obtained. Taming the flexible swept wing was a key enabler of modern large jet planes. Infamously the very earliest (first four I think) 747s built carried additional mass (in the form of depleted uranium) in the pylons to get the moment up to what was needed. This was additional to the depleted uranium used in other parts of the aircraft as counterweights that continued until the early 80’s. Next time you are on a larger aircraft, look out the window and look at the engine. You will see that it is gently nodding. This is the wing flexing with its period controlled by the engine mass on the pylon. On a 4 engined plane the engines on each side nod slightly out of phase, following the phase lag of the twist along the wing member. My source is Wide-Body: The Triumph of the 747, by Clive Irving. Which is a really good read. [Previous page](https://boards.straightdope.com/t/modern-engine-innovations/980823.md?page=2) [Next page](https://boards.straightdope.com/t/modern-engine-innovations/980823.md?page=4)