What if you make the pistons magnetic, the cylinder block ceramic, and place a ceramic-and-copper-winding insert into each cylinder?
Am I missing something?
The effort taken to drive an alternator is mostly the effort required to generate electricity and modern cars need a lot. Generating that electricity will take the same power however you do it, so the only savings would be the losses incurred driving the belt and the pulleys.
If the magnetic field was going to induce a current in the COPPER , what was to stop the same magnetic field inducing currents in the aluminium ?
You’ve then just added a lot of mass and cost just to replace an alternator.
I think you’re probably looking for something like a free piston linear generator. This can potentially eliminate all rotating hardware; if a two-stroke design is used, then you don’t even need valves for gas exchange. A four-stroke design can be implemented using intake/exhaust valves that are electrically or hydraulically actuated by the ECU (depending on whether you are using the engine to generate electrical or hydraulic power), eliminating even the camshaft.
Controlling a free-piston engine is difficult. Because the piston is (by definition) not mechanically constrained, it’s possible for it to mechanically impact at either end of its stroke if you don’t extract enough power on the power stroke (or admit enough air prior to the compression stroke). Alternatively, if you extract too much power during the power stroke (or admit too much air prior to the compression stroke), the piston won’t travel far enough to complete the next event. So a robust free-piston engine requires real-time measurement and analysis of piston speed/position and combustion chamber pressure, and the ability to modify the gas exchange and power extraction processes on the fly.
An magnetic piston within a coil would be a good implementation of a free piston engine in order to control the piston movement. The engine would also be a gas generator and could drive a turbine generator.
Reciprocating engines are inherently inefficient. much better to do a rotary design (wankel or turbine). As others have mentioned, the fuel cell looks attractive-but they seem to have stalled, developmental wise. I did read about the attempts to develop the Stirling cycle generator-it failed because of the unreliability of the seals in the engine.
ralph,
Wankels and turbines are less efficient than piston engines.
Are you sure? You need a heavy crankshaft plus a linkage for valves.
A Wankel is less efficient than a conventional reciprocating-piston engine primarily because of the large surface-area-to-volume ratio of its combustion chambers; a greater proportion of heat from the combustion gases is lost to the rotor and housing before it can be converted to mechanical work during the expansion stroke. the surface area per unit volume trend also shows up in reciprocating-piston engines of different configurations, e.g. a 2.4L V6 is likely to be less efficient than a 2.4L I4 at the same power output. There are other practical matters that make the Wankel problematic, e.g. sealing and durability.
Gas turbine engines can give good efficiency at their design load, but they have much more limited efficiency at low-load operation (as compared to piston engines). They are a good choice in applications that have a relatively steady power requirement, e.g. cruising jetliners or stationary power generation, but a poor choice for most automobiles, which spend a fair amount of time at idle. The advent of hybrid-electric drivetrains (which can make use of an engine that runs at a more steady power output) may make small gas turbines a viable option for passenger cars, if manufacturers can figure out how to keep them quiet.
Efficiency is one of many considerations for an engine; there are a zillion high-efficiency concepts out there that have had a lot of money thrown at them, but most don’t make it to production because of some other reason: reliability, weight, cost, maintenance requirements, durability, noise, etc.
yes, I’m sure. both Wankels and turboshaft engines have higher brake specific fuel consumption. The Wankel suffers because the combustion chamber has a large surface area for heat to be lost to the coolant. Turboshafts lose a lot of heat out the exhaust.
as an example, the last Mazda RX-8 was 500 lbs lighter and had a little over half of the horsepower than the concurrent Mustang GT, but got similar to poorer fuel economy.
what they do have to their advantage is power density or power-to-weight ratio.
IC engines are, like most things, heat engines. Ultimately the thermodynamic efficiency constrains what you can do, and no amount of care and feeding of the bearings, driven ancillaries, and the like can get you past this. Modern reciprocating ECSs can already get as close as any other technology to their ultimate efficiency. Unless you have design that addresses this, you are not contributing anything useful.
The single biggest thing is combustion temperature. The higher the better. Losses in the combustion chamber already start to kill your efficiency here (as pointed out, Wankel rotary and others). This was one place where a ceramic block and head were supposed to make a difference - as they could allow for significantly increased engine temperatures, but that technology never seemed to work out. Diesel and especially turbocharged diesel are the big win here - as the combustion temperature is significantly hotter than gasoline, and that directly turns into higher efficiency. After that, getting the exhaust temperature as low as you can gets you efficiency at the other end. For a car there isn’t a lot you can do here.
Large diesel engines (ie in ships) are about the most efficient engine we can build (with the caveat that it makes useful amounts of power). Roughly 50%. Which is astounding. You get close to that with a steam turbine in a power station, but that needs major cooling (hence those huge towers) to get the efficiency up - they cool the exhaust steam so well it condenses to water and the turbines exhaust into what is close to a vacuum.
The lesson is that there really is no point looking at the wizzy bits in an engine to find big wins in efficiency. Small incremental ones yes, but any sort of ground breaking improvement isn’t going to come from here. The efficiency is dominated by what you can do in the combustion chamber.
One big problem, IIRC, was volumetric efficiency: because the incoming air got heated by the extremely hot surfaces of the intake port and combustion chamber, it was low density, and so you couldn’t get much air (and so not much fuel) into each combustion event, resulting in disappointingly low power density.
Diesels have a few things going in their favor, but combustion temp isn’t one of them. What makes Diesels efficient:
Lean Combustion
Whereas gasoline spark-ignited (SI) engines usually run at or very close to a stoichiometric A/F ratio, diesel compression ignition (CI) engines run very lean most of the time, only getting close to stoichiometric when they are making peak power. The excess air acts as a diluent, soaking up heat and reducing peak temperatures, which in turn reduces thermal losses to combustion chamber surfaces and keeps that heat around for conversion to mechanical work during the expansion stroke.
Unthrottled Gas Exchange
CI engines have no throttle plate to restrict the pumping action of the pistons. The throttle on an SI engine is a significant source of inefficiency for SI engines at anything other than wide-open; just like trying to breathe through a straw instead of through a big ol’ pipe, the engine expends energy trying to inhale through the throttle restriction.
High Compression (expansion) Ratio
Because SI engines premix the fuel and air and rely on a spark to control ignition timing, they are unable to utilize the high compression ratios that would confer better efficiency. CI engines require a high compression ratio for ignition purposes, and the resulting high expansion ratio means more of the combustion heat is converted to mechanical work during that expansion stroke. As it happens, the real-world optimal compression/expansion ratio is somewhere around 14:1; if you go higher than that, your thermal losses to the cylinder/head exceed the gain in efficiency you get from the higher expansion ratio. Small CI engines, like Volkswagen’s little TDI, need higher compression ratios (~19:1, IIRC) in order to ensure reliable cold-starts; if they could adjust their geometry back to 14:1 compression after a cold-start, they’d be even more efficient. Larger diesels (e.g. the monster marine-diesel engines) have a low surface-area-to-volume ratio, so they can be designed with a compression ratio much closer to 14:1 while still providing reliable cold-starts.
Well said, Francis.
Whenever you think of introducing radical new engine technology, you have to look at what you have to beat. Here’s one example, the Audi 2-litre TFSI engine, which puts out no less than 200HP. It is a sophisticated beast, the product of 100 years of incremental development of the piston & cylinder concept. Just look at the list of technical cleverness, including variable intake valve timing, and a variable length controlled intake manifold.
I use this engine as an example because I happen to own a specimen of it, and it is a thing of joy. Almost silent, and low-rpm torque like a steam engine.
I think it is not properly understood that a piston & cylinder engine is inherently easier to make, because in sealing piston and cylinder you only have to solve a 1-dimensional sealing problem. (the same problem all round the piston circumference) In a rotary engine you have to solve a 3-dimensional sealing problem, and that is the main reason that rotary engines, of whatever type, have never got anywhere and probably never will.
You make a disadvantage sound like an advantage :). Diesels cannot run stoichiometric because they are more likely to have incomplete combustion and make soot or smoke - so they need excess air. Running near stoichiometry has the potential for the highest efficiency since the temperature is the max and by definition the thermodynamic efficiency.
Also - since Diesel engines are forced to run lean to avoid soot, they inturn produce more NOx (pollutant) compared to the gasoline engines. You have more air (and hence more nitrogen) around the combustion - so you get more NOX.
this is one reason gasoline direct injection is starting to shine. Some models in Mazda’s SkyActiv gas engine family run 14:1 static compression. the evaporation of the fuel in cylinder helps ward off preignition/detonation.
plus, turbocharged gas DI engines (GTDI) have eclipsed diesels in torque output and way outclassed them in horsepower. I snicker when I hear a VW/Audi TDI owner natter on about how “torquey” their engines are, while pretty much every 2.0 liter GTDI engine on the market has a lot more torque and WAY more horsepower than the VW diesel.
take a look here, and work through the math: the efficiency of a CI engine is a function of compression ratio and cut-off ratio, where cut-off ratio is related to the duration of combustion (i.e. how far it overlaps with the expansion stroke). If you add more fuel, it takes longer to burn, and the theoretical max efficiency actually goes down.
That’s not even considering the real-world fact that high peak temperatures result in increased heat loss and consequently reduced efficiency. Do a google-image search for a diesel engine efficiency map, and you will see that peak efficiency always occurs at something less than maximum load.
Note also that for the theoretical Otto cycle, which assumes instantaneous combustion at TDC, the peak temperature doesn’t even figure into efficiency. See equation 6 at that link: the theoretical maximum efficiency is defined entirely by the compression ratio, meaning if heat loss to the combustion chamber weren’t an issue, you could burn stoichiometric (high peak temp) or lean (low peak temp) and expect the same efficiency either way. Since heat loss actually does matter, lean-burn wins, at least as far as efficiency is concerned. The high NOx output that comes with lean-burn is yet another one of those annoying real-world issues that gets in the way of maximizing efficiency.
Take a look back at your own link:
Bolding mine - illustrating that stoichiometry (air-to-fuel ratio plays a big part 
Could you please rethink what you are saying ?
I suggested you work through the math. If you had done so, you would have found that for increasing adiabatic flame temperature, the theoretical maximum diesel cycle efficiency actually decreases slightly - contrary to your claim upthread.
Seriously, put the equations in a spreadsheet, try various values for T_3, and see what it actually does to efficiency.
What I am saying is that the peak combustion temperature is almost completely irrelevant to the diesel cycle’s theoretical maximum Carnot heat-engine efficiency, except when considered in the context of the temperature at the end of the expansion stroke - and in the theoretical diesel cycle, the relationship between those two temperatures is almost completely dictated by the compression (expansion) ratio. To the extent that peak combustion temperature is relevant to theoretical diesel cycle efficiency, increasing it actually decreases efficiency, contrary to what you’ve been claiming. If you still disagree with that, I can only assume it’s because you haven’t done the math.
I am further asserting that in the theoretical Otto cycle, the relationship between those two temperatures (and therefore the theoretical maximum efficiency) is completely dictated by the compression (expansion) ratio. If you disagree with that, you’ll have to explain where peak combustion temperature appears in equation 6 on this page.
