# 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:** 4
**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, 11:53am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/61 "2023-04-09T11:53:11Z")
Beyond @Francis_Vaughan’s excellent points, thrust asymmetry in a failure is not _that_ big a deal. You make the vertical fin/ rudder a bit bigger and you’re done. Conversely, if you switch to tail-mounted engines you _could_ shrink the tail & save the weight and drag. Except … Now the thrust reversers disturb the airflow over the tail and the fin/rudder is ineffective at controlling your path during rejected takeoffs and ordinary landings. The MD-80 suffered grievously from that. Compared to the DC-9 the engines were much bigger with much more reverse thrust in a larger plume. But the tail was the same size. There were lots of restrictions on limiting reverse thrust lest the airplane get squirrelly on landing. Every MD-80 driver, including me, has felt the damn thing start going sideways after you overdid the reverse a bit in a crosswind. Rear-mounted engines also pretty well require a T-tail or at least a cruciform tail. The rudder/fin structure required to carry the horizontal stab/elevator loads to the fuselage is a LOT heftier than you might expect. The inside of the vertical fin on a 727 or MD-80 looks like it belongs in a railroad bridge, not a flying machine. The 737’s fin innards look positively delicate by comparison. There are more factors to the decision, but I’ll quit now. Bottom line: tail-mounted engines are no free lunch. ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [April 9, 2023, 11:59am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/62 "2023-04-09T11:59:08Z")
> [@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. > [@Machine\_Elf](#): > > Large bore engines are also the ones in which you would see the most gain from having two spark plugs per cylinder I just bought a new Ram pickup with the 6.4L gas engine. It has two plugs per cylinder. In keeping with the thread subject, it has 410 hp. My 2000 model pickup with 7.3L had 295 hp. In the 70s I was a part-time mechanic (at a filling station). I’m familiar with ICEs and have rebuilt a few. But I literally cannot identify many of the objects, mysterious piping and one entire assembly (the size of a breadmaker) in the new truck. It’s demoralizing that I have no idea what these things are. ---
**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:** [April 9, 2023, 1:28pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/63 "2023-04-09T13:28:05Z")
Thanks to @LSLGuy for filling in the details. It is 40 year old technology, (Yipes! indeed) so it may have taken me a while to find references. As ancient as the technology seems it arose in the age of distributor ignitions on car engines. There’s a large window of time available for the spark compared to how long it takes for complete fuel combustion and the multiple sparking could insure complete combustion and overcome problems with water in the fuel or air that would slow ignition. Small planes had their own water problems with ice accumulation in common carburetors. I don’t know if these ignitions were accepted as safe in airplanes, it was argued that they were more reliable at keeping an engine running than the brief spark provided magneto ignitions. Similar considerations applied to the use of electromechanical fuel injectors for a diesel aircraft engine. They were considered less reliable than mechanical injectors activated by a cam shaft connected to the engine crankshaft. The new design used independent injectors that alternated on each cycle. Some failures could be detected and the remaining injector could be run on every cycle. If failures went undetected the engine would keep running even if fuel was injected only every other cycle. ---
**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:** [April 9, 2023, 3:33pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/64 "2023-04-09T15:33:30Z")
> [@md-2000](#): > > Obviously the wing spar needs to accomodate the engine weight and so the longer the spar out to the engine, the more weight. Keep in mind that when a plane is flying, it’s the wings that are holding up the fuselage, not the other way around. Moving heavy stuff, like fuel and engines, to the wing means that the spar is carrying a lighter fuselage. ---
**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 11, 2023, 12:45pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/65 "2023-04-11T12:45:16Z")
Thanks for all the info. Obviously, there are second and third order engineering considerations that begin to matter at extremes of weight, speed, etc. > [@TriPolar](#): > > As ancient as the technology seems it arose in the age of distributor ignitions on car engines. There’s a large window of time available for the spark compared to how long it takes for complete fuel combustion and the multiple sparking could insure complete combustion Just as an interesting point, I many years ago bought an old VW Beetle (my first car) and adventurously tried to do my own tune-up. I inadvertently swapped the spark plug leads on one side, and the car ran fine until it approached 30mph and began to get rough - giving you an idea how forgiving the spark timing could be and still work. Whereas I was told (never verified) that my early Honda Civic simply doubled up the sparks - fired 2 of 4 plugs at a time, simplifying the electronics; since one of those plugs was on the exhaust cycle and a spark had no effect. ---
**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 12, 2023, 1:36am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/66 "2023-04-12T01:36:05Z")
> [@md-2000](#): > > Whereas I was told (never verified) that my early Honda Civic simply doubled up the sparks - fired 2 of 4 plugs at a time, simplifying the electronics; since one of those plugs was on the exhaust cycle and a spark had no effect. I had a 4-cylinder 125hp outboard motor that worked the same way. Two coils, each attached to two plugs. When the coil was triggered, the two plugs in separate cylinders fired. The one plug did something useful and the other one did nothing in the middle of exhausting. ---
**Author:** ![its\_the\_daddy](https://avatars.discourse-cdn.com/v4/letter/i/bb73d2/32.png) [@its\_the\_daddy](https://boards.straightdope.com/u/its_the_daddy)\ **Post date:** [April 12, 2023, 5:59am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/67 "2023-04-12T05:59:20Z")
It’s called a ‘wasted spark’ system: not at all uncommon. > **[Wasted spark system](https://en.m.wikipedia.org/wiki/Wasted_spark_system)** > > A wasted spark system is a type of ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a cylinder on its exhaust stroke. The extra spark during the exhaust stroke has no effect and is thus "wasted". This design halves the number of components necessary in a typical ignition system, while the extra spark, against much reduced dielectric resis... ---
**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 12, 2023, 6:58am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/68 "2023-04-12T06:58:10Z")
> [@md-2000](#): > > Whereas I was told (never verified) that my early Honda Civic simply doubled up the sparks - fired 2 of 4 plugs at a time, simplifying the electronics; since one of those plugs was on the exhaust cycle and a spark had no effect. My first BMW motorcycle (a '99 model with a boxer twin engine) had the spark plugs for both cylinders on the same coil and fired them on every crank revolution. It also fired both fuel injectors on every crank revolution. This alleviated any need for a cam position sensor. ---
**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 12, 2023, 1:00pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/69 "2023-04-12T13:00:36Z")
> [@Machine\_Elf](#): > > It also fired both fuel injectors on every crank revolution. You’re the pro here, not me. But that sounds like they’d be pissing away 50% of all the fuel. Giving half the fuel mileage and lots more than double the air pollution. That seems … un-German. Have I misunderstood? ---
**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 12, 2023, 1:16pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/70 "2023-04-12T13:16:29Z")
> [@LSLGuy](#): > > You’re the pro here, not me. > > But that sounds like they’d be pissing away 50% of all the fuel. Giving half the fuel mileage and lots more than double the air pollution. That seems … un-German. > > Have I misunderstood? Since any given cylinder’s fuel injector squirts twice for each complete four -stroke cycle, that just means each injection event needs to supply half of the required fuel for that cycle. These are port fuel injectors, so no fuel gets into the combustion chamber until the intake valve opens and the intake stroke of the piston happens. Maybe you were thinking of direct fuel injection (in which the fuel injectors fired directly into the combustion chamber)? ---
**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 12, 2023, 1:35pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/71 "2023-04-12T13:35:15Z")
I’d assumed it was DFI, yes. Port fuel injection is so … 1970s. Or so I thought. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [April 12, 2023, 4:09pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/72 "2023-04-12T16:09:40Z")
> [@Stranger\_On\_A\_Train](#): > > The supposed “world wide switch to electric power” is going to be the work of several decades, and there are still going to be niche applications where mobile power generated by combustion engines of some form will be necessary (specifically aircraft and heavy shipping), as well as the fact that most electrical power production besides PV solar, wind, and tidal are via heat engines in some form. I’ve seen some arguments that trucking and vehicles for cold weather climates might be better to run on hydrogen than electric. > **[Hydrogen fuel cells seek transport niches EVs can’t reach](https://www.reuters.com/business/energy/hydrogen-fuel-cells-seek-transport-niches-evs-cant-reach-2022-11-09/)** > > Hydrogen fuel cells are losing the battle against lithium-ion batteries in cars and light transport, but as hydrogen prices come down, the technology may find a niche in longer-haul, heavy-load transportation. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [April 12, 2023, 5:13pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/73 "2023-04-12T17:13:10Z")
> [@Sage\_Rat](#): > > I’ve seen some arguments that trucking and vehicles for cold weather climates might be better to run on hydrogen than electric. Well, that might be true if the cost of catalysts for hydrogen fuel cells goes down and the production and logistics issues of hydrogen fuel are resolved. I am not convinced that this will ever be the case without substantial improvements in both catalysts and storage density of hydrogen. Stranger ---
**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 12, 2023, 11:12pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/74 "2023-04-12T23:12:58Z")
> [@LSLGuy](#): > > I’d assumed it was DFI, yes. Port fuel injection is so … 1970s. Or so I thought. Gasoline direct injection is a mixed bag, which is probably why there aren’t many of them out there. The Wikipedia page doesn’t include a bookmark for the “Disadvantages” section, but if you scroll down, you’ll come to it: > **[Gasoline direct injection](https://en.wikipedia.org/wiki/Gasoline_direct_injection)** > > Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold (inlet manifold). > The use of GDI can help increase engine efficiency and specific power output as well as reduce exhaust emissions. > The first GDI engine to reach production was int... ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [April 13, 2023, 10:10pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/75 "2023-04-13T22:10:50Z")
> [@Stranger\_On\_A\_Train](#): > > Well, that might be true if the cost of catalysts for hydrogen fuel cells goes down and the production and logistics issues of hydrogen fuel are resolved. I am not convinced that this will ever be the case without substantial improvements in both catalysts and storage density of hydrogen. PGMs are a minor contributor to the cost of a PEMFC system, which is dominated by balance-of-plant components like electronics and plumbing. And catalyst loadings keep decreasing. I agree hydrogen logistics are a barrier. ---
**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 20, 2023, 8:59am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/76 "2023-04-20T08:59:08Z")
Toyota is coming out with a hydrogen-powered car. But it doesn’t use fuel cells. It uses a hydrogen internal combustion engine. I didn’t know it was possible to make an ICE that burns hydrogen. [Corolla Cross H2 Concept](https://www.cnet.com/roadshow/news/toyota-corolla-cross-hydrogen-combustion-concept/) ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 20, 2023, 11:00am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/77 "2023-04-20T11:00:18Z")
> [@Stranger\_On\_A\_Train](#): > > Well, some are. However, even if the developed world goes full tilt on producing electric vehicles there are supply limitations for both the batteries and motors, and **the developing world doesn’t have the infrastructure to support reliable mass electrification** Bold mine But is that infrastructure needed? Mass production of EV’s means even 3rd world countries will be buying used EV’s, or at least electric drivetrains eventually and will make them work as that will be all that is available. Even if this means putting a generator on the roof, or perhaps recharging with used solar panels. As for supply limitations, we are just starting to mine lithium, not too long ago no one did, but lithium was just a byproduct of other mining. Now that the free markets are actually looking for it it seems like it will be found. So what seems somewhat rare today might not in a decade. ---
**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 20, 2023, 11:37am UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/78 "2023-04-20T11:37:22Z")
> [@Crafter\_Man](#): > > … I didn’t know it was possible to make an ICE that burns hydrogen. > > [Corolla Cross H2 Concept](https://www.cnet.com/roadshow/news/toyota-corolla-cross-hydrogen-combustion-concept/) Burning hydrogen is by far the easiest thing to do with it technologically. Much easier than, e.g. running a fuel cell with it. At least from where our deployed tech is today. If an ICE can run on gasoline or propane or methane (AKA “natural gas”) with comparatively minor tweaks, it can certainly be so tweaked to run on hydrogen. The same is true of gas turbines used in some ships and all modern airplanes. As with propane/methane, the practical challenge is _not_ in building _an_ engine to burn it. It’s in designing and deploying the infrastructure so millions of those engines can be supplied with fuel every day. But most of those challenges aren’t technological engineering. They’re cost-effectivity engineering and financial engineering and legal engineering. Which are often the three hardest kinds. ---
**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 20, 2023, 12:12pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/79 "2023-04-20T12:12:30Z")
> [@Crafter\_Man](#): > > I didn’t know it was possible to make an ICE that burns hydrogen. Hydrogen has a really high octane rating, so you can design the engine to operate at a higher compression ratio (and therefore a higher efficiency) than is typical for gasoline engines. Using hydrogen obviously means no carbon. Whether there’s no CO2 associated with operating this engine will depend on how the hydrogen fuel is produced, but you definitely won’t get any CO2, CO, raw hydrocarbon, or particulate matter out of the tail pipe. (Ok, maybe you’ll get a smidge just from crankcase oil that gets burned, but it won’t be much.) OTOH, the laminar flame speed for hydrogen is many times that of gasoline (about 3 m/s, versus about 0.4 m/s for gasoline). This has consequences for the rate of pressure rise during the combustion event: high rates of rise manifest as audible roughness, the kind of sound you hear from a diesel, which a lot of drivers don’t care for. There’s also the question of range. Since you can’t use liquified H2, it’s hard to store enough fuel onboard to go very far, unless you are willing to use a hybrid drivetrain to maximize fuel economy. But the article you linked to says that Toyota is specifically avoiding going electric on their H2 Corolla, so I wonder what kind of range it has. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [April 20, 2023, 12:31pm UTC](https://boards.straightdope.com/t/modern-engine-innovations/980823/80 "2023-04-20T12:31:56Z")
That was my guess too - specifically considerably higher compression ratios, along with variable ignition timing and computer-controlled fuel injection. It seemed to me having driven some mid-late 1970s and early 80s junkers, that power _really_ improved once fuel injection became normal, and along with it computer control of the engine. > [@EinsteinsHund](#): > > The obscenely giant (and thirsty) 8 cylinder engines with rather low horsepower were almost exclusively an American phenomenon at that time. European and Japanese auto builders got much more horsepower out of much smaller engines even then. US manufacturers _could_ make more power- the original Chevy 350 as used in the 1969 Corvette had a 11:1 compression ratio and used high octane gas, to give 350 horsepower. But, like others have pointed out, the emissions regulations in the 1970s crippled the power output of the older design engines, so there was a period of really anemic engines until the mid-late 1980s, when fuel injection and computer control came into production and power jumped back up. Since then, it’s been incremental improvements- variable valve timing, four valves per cylinder, direct injection, and so on. [Previous page](https://boards.straightdope.com/t/modern-engine-innovations/980823.md?page=3) [Next page](https://boards.straightdope.com/t/modern-engine-innovations/980823.md?page=5)