New Mars Forums

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,583

Re: Fixing Americas car industry

tahanson43206,

If you're willing to "reserve" 3m^3 out of 215.05m^3 as unusable tank capacity, to allow you to operate the air turbines at 180psi vs 90psi, then your air consumption rate is cut in half.

58.5cfm / 4.5kW = 13cfm/kW
13cfm * 60 minutes = 780ft^3 per kWh
212m^3 / 22.0871m^3 per kWh = 9.598kWh
Edit:
505.15595kg / 9.598kWh = 52.631kg/kWh <- Substantially lower than the Lithium-ion battery pack on its own, in order to achieve 25,000 duty cycles before unacceptable degradation occurs for either the compressed air tank or the Lithium-ion battery pack

Your air turbine(s) might benefit from 1 or 2 additional expansion turbine blade-disks / "blisks" to extract more energy from air expansion, but you get 39% more energy to work with by regulating air pressure at 180psi (12.4bar) vs 90psi (6.2bar).  There's obviously a practical limit as to how high you can go, and higher pressure equals more noise, but there are various commercial air tools which consume higher-psi air.

This would negate or offset any advantage Lithium-ion batteries provide, in terms of weight, if both technologies are expected to provide 25,000 duty cycles before they have to be taken out of service and replaced with new equipment.

Edit #2:
If you doubled the regulated / operating air pressure again, to 360psi, then you give up 6.28m^3 of tank capacity (the volume and weight of air in your storage tank which would be below your regulated air pressure), but your air consumption rate is cut in half again.  Your tank's service life benefits from a less extreme pressure cycling as well.

215.05m^3 (at 850bar) - 6.28m^3 ("lost" to operating at 360psi / 24.8211 = 208.77m^3
6.5cfm * 60 minutes = 390ft^3 per kWh
208.77m^3 / 11.0436m^3 per kWh = 18.834kWh
505.15595kg / 18.834kWh = 26.821kg/kWh

Our compressed air's gravimetric energy density, relative to a Lithium-ion battery capable of surviving for 25,000 duty cycles, is now more than twice as good.  At this point, we would definitely require a bespoke air expansion turbine design with more stages.  Let's say our lighter air powered car requires 150Wh per mile, and we're no longer going to bother with the additional complication of a flywheel to conserve energy.

18,834Wh / 160Wh per mile = 117.7125 miles of driving range

If power was directly proportional to weight, then it should require 139Wh per mile, but I presume some inefficiency of air vs electricity.

Anyway...  I hope this makes sense to you.

Last edited by kbd512 (2024-06-29 11:24:04)

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,583

Re: Fixing Americas car industry

In gas turbine engines, the overall pressure ratio is a major factor in fuel efficiency- just as in a piston engine, a higher compression ratio yields more efficient utilization of the energy contained within the fuel and air being combusted.  For the air powered car's power turbine(s), rather than compressing and heating up incoming air by burning fuel, we're instead starting with highly compressed air which we're expanding through what would be the hot section and expansion turbine stages of a conventional gas turbine engine.  If you start at a higher operating pressure, then you can add a greater number of expansion stages for substantially greater efficiency.  Doubling the regulated air pressure fed into the turbine inlet halves the airflow rate for the same work done, so you gain quite a lot in terms of efficiency.  The downside is that you start giving up capacity within your storage tank, and the noise produced starts to sound an awful lot like a conventional gas turbine engine.

If the regulated / working air pressure was set to 360psi, then the mass of air in the storage tank which remains below 360psi cannot be properly expanded through a turbine designed to operate with a 360psi inlet pressure.  Similarly, conventional turbines violently surge or chug when smooth airflow through the core becomes turbulent, because that condition is associated with a pressure loss.  The blades which extract energy from the air are shaped to work optimally with air at a given velocity and pressure.

To counteract this loss of air tank capacity, you could run multiple turbines optimized to operate at different regulated pressures to fully consume all of the air in the storage tank, especially since they're so light and compact.  This still unavoidably adds some weight, complexity, and cost.  However,  even if this vehicle is primarily air-operated, all of its lights, heater, and any personal electronic devices, such as cell phones, all require electrical power.

I don't think I initially understood tahanson43206's point about electrical brakes.  If he meant this new "brake-by-wire" system, then no, this vehicle will not have any of that ridiculous nonsense.  If he actually meant an anti-lock braking system, then yes, this vehicle will use sensors and a computer to apply and release the brakes many times per second when the driver presses down on the brake pedal, in order to avoid wheel lock-up and skidding.  ABS with ESC is required on all passenger vehicles made after 2012.  Airbags were required since 1998.  The cost of both systems is nominal, about $500 to $750, and the reduction in fatalities is very real, so these systems will be incorporated into the vehicle design because they don't materially affect the per-unit price the way using large quantities of Aluminum or Carbon Fiber do.  All told, the safety equipment on a modern vehicle is a small portion of its total cost.

That said, the vehicles themselves and their restraint systems are what should protect their occupants in a crash.  Air bags are a band-aid for poor restraint systems.  Fatal accidents during racing are nearly unheard of these days, yet none of those race cars have air bags or ABS.  ABS and ESC are driver aids for people who generally lack quick decision making and skill at driving.  Motor vehicle fatality rates have stagnated since the end of the 1990s, following the introduction of air bags and ABS with ESC.  More recently, motor vehicle fatality rates are rising again, because all vehicles have become so ridiculously large and heavy, relative to the 1990s.  Pedestrian fatalities and fatalities from the monstrosities that cars and trucks have become is on the rise again.  Large trucks and SUVs, falsely marketed as "being safe" (because they are large and heavy), all compare unfavorably to smaller and lighter sedans with a lower CG, meaning they score the lowest on NHTSA crash testing.  All of that tells me that much of the supposed benefits of these "safety devices" or "safe heavy vehicles" are a poor substitute for the loss of common sense while doing something potentially dangerous, such as driving a large and heavy motor vehicle.

Anyway, the point is that these vehicles will still have the government mandated safety devices to prevent skidding and wheel lock-up.  If I can figure out how to do the same thing without using electronics, then no electronics will be used where none are required.  ABS, for example, doesn't specifically require electronics to do what it does, because the only thing the sensor does is translate a sine wave into decisions about hydraulic valve actuation.  If you have permanent magnets that actuate air valves to apply and release the brakes, that can be done just as fast as any electro-hydro-mechanical system does it, but likely faster, because air brakes can be actuated and released faster than hydraulic brakes.  The yaw rate sensor incorporated into ESP (Electronic Dynamic Stability Program) can also be entirely mechanical.  ESP uses sensor input to determine if a vehicle is swerving or skidding relative to the steering input, and applies power or brakes to the other wheels to correct it.  Every Cessna 172 I've flown came equipped with a highly accurate yaw rate sensor that wasn't electrically powered, and because it didn't require electricity, was completely unaffected by electronic glitches or loss of electrical power.

Using compressed air and magnets, we can achieve what the electronics do, but retain the ability to troubleshoot the system without more sily electronics.  Boeing has already achieved "peak stupid" with electronics.  We don't need more stupid.  We need more recognition of the limitations of every system.  We must then accept that adding more of what's already causing so many problems that the engineers who designed those systems cannot solve the problem, is not going to help, it's merely creating new problems which didn't previously exist.  This is coming from someone who makes his living using computers.  Given what I know about computers, I also know that further increasing the complexity of modern vehicle systems is not going to make them more affordable or more user-friendly for the average design engineer, mechanic, or driver.

All the endless tinkering with electronic control systems has not produced a more usable result, it's merely made the result unaffordable while ensuring that nobody actually knows what the software is doing, nor why, because no single person can keep track of all the moving parts involved.  Regardless of how outwardly simple an electronic device or sensor system running a software program appears, there's so much going on inside that you wouldn't believe it.  The simple fact that it works most of the time is the unbelievable part.  It's great until it fails, and then it's not, because nobody can actually "fix it", they'll merely replace it, and hopefully that solves the problem.  Firing the parts cannon at multi-thousand-dollar computers and battery packs is no longer a workable repair strategy.  This is my answer to people who think we merely need to add some more sensors and software.  Either figure out how to repair the system without replacing every bit of it, or you've reached the end of your rope with electronics.

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,583

Re: Fixing Americas car industry

Electronics Account for 40 Percent of the Cost of a New Car

While individual chips may be cheap these days, the computer's significance is evident in just how many there are in a single car. Electronics are responsible for 40 percent of a new car's total cost.

All I can think to myself is how ridiculous it is that 40% of the cost of a machine the size and weight of a motor vehicle, which is primarily intended to roll around on paved roads rather than to take people into space, is solely devoted to computerization of the vehicle.  Money is merely a proxy for energy and labor.  That means the energy and labor that went into making the computers and sensors are greater than any other single component on the vehicle, regardless of weight, what it's made from, or mechanical complexity.  For devices which represent such a small percentage of the total vehicle mass, and cannot be repaired at all, that's an unsustainable absurdity.  That Car and Driver article was written 4 years ago.  I'd be shocked if 50% to 60% of the cost of the latest vehicles isn't all the electronics they're equipped with.

A passenger car does not need more computers, sensors, and software than a Space Shuttle or a stealth vertical takeoff supersonic fighter jet with sensor fusion.  All the vehicles made before computers, which have outlived nearly all computerized vehicles by a half century or more, is prima facie evidence that such is the case.

The vehicles made during the 1990s were the high water mark for reasonable usage of electronics to improve the function of specific vehicle components, such as the engine or transmission or braking system.  Motor vehicle fatality rates have not improved since then, repair costs haven't improved since then, and vehicle longevity and total cost of ownership hasn't improved since then, either.  Total cost of ownership is another proxy for energy and labor usage.

Apart from machining tolerances, the most impactful changes to vehicle efficiency since the 1990s are that most modern vehicles are now powered by turbocharged 4-cylinder engines with half the displacement of V-8 engines while producing the same power output, along with increased compression ratios.

As far as vehicle emissions are concerned, when Speed of Air introduced pistons designed to completely combust more of the fuel, for diesel engines that single change resulted in lower emissions than the combination of particulate matter filters and diesel exhaust fluid (urea).  It reduced NOx, PM2.5, and CO to below the levels produced by all the emissions systems fitted to modern diesel powered vehicles.  The greatest emissions reductions will not be achieved by improving or adding more electronics to the engine, but by increasing the efficiency of the fundamental processes which make the engine run.

High-Tech Cars Might Be More Trouble Than They’re Worth

Drivers may sacrifice safety and privacy in exchange for the advanced tech features in their "smart" cars

Modern cars are often described as "computers on wheels." They come with automated driver assistance systems, large display screens, Internet connections and a multitude of ways to sync with smartphones.

Yet in the rush to innovate and one-up competitors with ever newer technology, things may have gone too far. Some developments have made driving safer, but others veer toward tech excess that can actually harm drivers. Cars in the current generation can be pricier to repair, harder to understand and operate and, some experts in the field say, more likely to cause distraction and driver disengagement.

The Threat Behind Computerized Vehicles

The idea behind vehicular attacks is simple. Unlike conventional weapons, larger cars and trucks are more ubiquitous, and the potential cost to morale and the population as a whole is high. The main concession is that these transports need to be manned by a person with devious intent. However, the continued computerization of vehicles, as well as the push towards complete autonomous driving, may make this form of improvised ammunition much more effective and dangerous.

If we were serious about reducing motor vehicle fatalities, then we would accomplish that by mandating 7-point harnesses and racing helmets.  Almost nobody dies in racing following 200mph impacts with walls that won't even budge when the race cars hit them.  Most of the time, the drivers walk away from those horrific-looking accidents.  The car is an absolute mangled mess, but other than being badly shaken up by the experience, the driver will frequently run away from their race car afterwards.  If you won't accept those concessions to your "driving comfort", then accept that you don't actually care about your own safety as a motorist, you just want to spend money on electronic devices which make you "feel" as though you're in less danger than you truly are, which hopefully will reduce the severity of your injuries in a major accident, but will never provide a fraction of the protection of proper restraint systems and roll cages.  A vehicle built like a "stock" racing car is the only kind of vehicle wherein you can have a head-on collision with a semi-truck and literally walk away from it most of the time.  There are no absolute guarantees in life, but I would never want to be in any kind of "modern" or "classic" as-built passenger car in that situation.

The materials used to fabricate stock cars are lightweight steel tubing under fiberglass bodies, low-cost except for the labor used to weld the tubes together (which obviously can be and has been automated), and oddly enough, no computers are required to make them function as they do.  All the bits and pieces that make them so performant are either purely mechanical or electrical for the ignition system only.  Adding more electronic nonsense to a vehicle doesn't make it perform any better.

Every vehicle equipped with a catalytic fuel converter runs with a sub-optimal fuel-air ratio, almost 100% of the time, because they deliberately oscillate back-and-forth between too-rich and too-lean, in order to make the catalytic converter function.  Speed of Air did with CFD-optimized pistons, what none of the major OEMs ever did with catalytic converters, diesel exhaust fluid, and particulate matter filters.  This is indicative of the difference between a high quality mechanical design and the various electronically-controlled band-aid solutions added to existing products.

It would not matter in the slightest if we used computers or a new piston and valve train design to clean up the combustion process, except that the "golf ball" piston design would burn significantly less fuel, produce fewer emissions, and provide more power throughout the entire engine rpm range, which would increase the life of the engine so that a new one would not need to be built.  That new piston design also greatly reduced soot in the oil, doubling the oil change interval up to what Caterpillar mandated as their maximum allowable oil change interval, without resorting to using solid rings, and worked equally well with Aluminum and "Monotherm" steel pistons.  The tech was originally created to reduce emissions from gasoline engines, but worked even better with diesel engines.

If we have all this wild new computer tech at our disposal, then we should be using it to create improved designs that don't have the problems computers were added to rectify in the first place.  The same applies to the air powered car.  Whatever we can do with our computers to improve upon the fundamental turbine and brake design, we're going to make those improvements first, and then resort to computer controls for any systems for which there are no worthwhile mechanical design improvements to be had.  That is the most appropriate way to go about automotive engineering.  You start with the most impactful but lowest cost solutions first, and then add higher cost components to meet design requirements if lower cost solutions are not feasible.