Heat Engines Part V - Innovative Internal Combustion Engines

Much more research and development has gone on in the field of internal combustion heat engines than the external combustion variety, and we believe that it is here that momentous changes are most likely to occur in the future. Quite a considerable number of startup companies are active in this space, and their activities are arguably at least as significant for the future of energy in transportation and small scale stationary energy transportation as are the endeavors of the fuel cell industry.

Before we explore the nature of some of the more interesting innovations, a word regarding the competitive position of next generation internal combustion and hybrid electric systems vis a vis fuel cells.

Hydrogen based fuel cells constitute an intriguing technology that may yet play role in the energy revolution we’re going to have to undergo. But the nature of their backers should give one pause. David Morris, head of the Institute for Local Self Reliance which is, the name notwithstanding, essentially a trade organization for ethanol producers, told us in an interview that almost everybody had lined up behind the hydrogen economy—the auto manufacturers, the oil companies, even the nuclear industry. Hmmm…. These are the guys that have been fighting like the devil for a green future all along, right?

If we ignore nuclear for a moment, an industry struggling for its very survival in the U.S., and instead we concentrate on the auto makers and the oil companies, we find it rather remarkable that either would embrace a successor technology at this point, particularly when there is a sufficient supply of heavy oil and oil shale to carry the transportation sector for many more decades. And we are not alone in our suspicions.

We believe, based on background interviews with both oil industry and auto industry insiders, that a number of factors are at work here.

In respect to the oil industry, hydrogen distribution could be made to fit within the same model used to distribute petroleum products today. That might not necessarily be the best model to pursue from an economic standpoint, but the oil companies are eager to promote it for obvious reasons. We are, however, extremely doubtful that the model will prove economically viable on any long term basis regardless of the wishes of the oil industry, a topic we will pursue in future posts.

Auto manufacturers are in a somewhat different position. From our perspective hydrogen fuel cells are a very long shot for a practical propulsion system because of numerous unsolved technical problems and because of the dubious economics of generating hydrogen from renewables. Their success would also require the auto manufacturers to phase out current tooling, some of which has been in place for decades. Particularly in America, archaic engine designs utilizing pushrods and other anachronisms continue to be manufactured today, and compared to European and Japanese manufacturers, Ford and GM have been very slow to innovate. For this reason some of our informants have suggested that the American auto makers actually have a very weak commitment to fuel cells and view the development projects as good public relations ploys that exempt them from improving either the fuel efficiency or emissions performance of ICEs (internal combustion engines).

We happen to believe that, absent unexpected breakthroughs in fuel cells and a major re-orientation of the fuel cell industry in a number of areas, fuel cells are likely to lose out to plug-in hybrids using new ultra-high density battery technologies and vastly improved ICEs. This will not happen quickly, however, because of the innate conservatism of any manufacturer owning vast, fully amortized production facilities and eager to placate stock holders by providing consistent short term profits rather than making heavy investment for the future. But of course one never knows. Given the turmoil in the American auto industry of late, a fundamental reorientation is possible if perhaps not likely.

That said, let’s look at what’s new and significant in ICE design.

ICE, ICE

ICEs form an enormously diverse body of design approaches, and, in coming to grips with that diversity, it helps to throw everything into two big piles—the truly radical machines and the variations on familiar approaches. The radical mechanisms represent a more or less complete rethinking of engine design while the second grouping consists of significant improvements on the existing art.

As a working taxonomy this two pile ploy is somewhat inexact because sometimes the improvements in old designs are themselves pretty radical while much of what appears to be truly radical total design concepts represents ideas that were conceived long ago and for one reason or another couldn’t be made to work at the time. In other words, some things could go in either pile. With that in mind, I’ll start to build the piles.

Most of the really radical approaches attempt to substitute rotary elements for pistons. These can be turbine blades, rotating vanes moving within a loop, or rotors describing eccentric motions that create variable volume cavities within an elliptical chamber. Also pretty radical are double ended pistons moving within a pair of opposing cylinders, a concept that has actually shown up in a couple of commercial designs.

The variations on a theme innovations include the Miller cycle, direct injection, and pulse detonation—mostly inventions impacting on the combustion process within engines of more or less conventional mechanical design.

There are also designs that simply defy categorization such as the OX2 which is an attempt to revive the old rotating crankcase engines used on some early aircraft.

Whether the design is radically new or simply a variation on a theme, the designer generally confronts one highly intractable conundrum, and one that has worked strongly against innovation in this field, and that is the fact that one nearly always faces a tradeoff between fuel efficiency and power density. Engines that crank out a lot of horsepower per pound such as Wankels, gas turbines, and two stroke gasoline reciprocating engines, generally have very poor efficiency, while highly efficient engines such as Miller cycle gasoline engines and four stroke diesels usually have low power outputs per unit of mass.

High energy density is generally a function of relative simplicity of design and fewer moving parts. This is certainly true of Wankels, turbines, and two strokes. Higher efficiency, on the other hand, is generally a result of optimizing thermodynamics rather than mechanical systems though certainly frictional losses ought to be minimized. Achieving relatively complete combustion, minimizing thermal losses, and harnessing the expansive powers of the gases of combustion to the greatest extent all play a role in maximizing efficiency. For a number of reasons which we’ll explore in due course, high efficiency designs tend to relatively large and heavy.

Lots of inventors claim to have achieved low power density combined with high efficiency but few have been able to back up such claims in the field.

The Really Radical Pile or Mostly Rotaries

All of the basic variants of rotary engines were developed in the nineteenth century and mostly applied to the steam engine. Except for the Parsons steam turbine, which became the basis for practically all modern coal and nuclear power plants, none of the other steam rotaries achieved even a foothold in the market.

Regarding the internal combustion rotaries there are two that might be deemed to be established in the market, the Brayton gas turbine and the Wankel.

The Brayton is well nigh ubiquitous today, forming as it does the basis of the turbojet and fanjet engines used in commercial and military aircraft. Braytons are also very extensively used in natural gas fired electric generator plants and to a limited extent in fast patrol boats and in a few yachts. They have seen very limited use in general aviation in turboprops.

Braytons at their simplest consist of two sections, a compressor and an expander, both of which make use of the aerodynamic lift created by a series of airfoils. In the compressor section the airfoils serve to draw in and compress the combustible fluid and air while in the expander the forces of combustion act on the airfoils.

Braytons are mechanically very simple but have traditionally been expensive to manufacture, the dozens airfoils each requiring precise machining and fitting as well as the ability to resist extreme thermal and mechanical stresses. To cite an example, within the general aviation market, a new Lycoming 200 horsepower certified reciprocating engine will run a little over thirty grand while a turbine of equivalent horsepower will cost about $200,000.

An American manufacture named Innodyn is aiming to achieve radical price reductions with an innovative turbine of their own design, but at this point the design is unproven in the marketplace. Innnodyn also claims to have successfully addressed another deficiency of the Brayton turbine, namely its poor fuel efficiency. The company claims to have achieved efficiency on a par with a spark ignition piston engine, which in truth is only fair and not good.

Other innovators, such as StarRotor, Jirnov vortex turbines, and TurbX claim much more substantial performance improvements and cost reductions based on far more radical designs, but unlike Innodyn, none of these companies is close to having a production engine. The manufacturing of engines is a very expensive business to enter, and to date only one radical design has ever achieved even limited success, namely the Wankel.

Wankel, the product of a self educated German mechanic named Felix Wankel, was invented in 1926, but Wankel, who was without means and was imprisoned for making anti-Nazis statements, was unable to bring his invention to market then or for decades after. Only in the nineteen fifties when he managed to interest NSU in the design did the necessary funding to productize the design become available.

The Wankel, which is in strictest terms a rotary piston design rather than a true rotary engine, is simple and compact and offers extraordinary energy density. Mazda has developed a racing version of their 13B design that puts out 900 horsepower at a weight of slightly over 200lbs, and some aftermarket modifications of the same engine top 1,400 horsepower. Overall durability of the engine is very impressive as well, although the seals on the rotor have tended to cause problems.

Fuel economy is the Wankel’s Achilles heel and traditionally it has not been much better than that of a simple Brayton turbine. The problem is inherent in the design. In a Wankel the rotating piston traverses the entire inner wall of the combustion chamber which constitutes a huge radiating surface. Thus heat of combustion is very efficiently transferred to the block which in turn reduces the pressure of the burning gas and thus the amount of mechanical work it can perform. Also, partially combusted gases are pushed out of the engine during normal operation due to very high engine speeds required to achieve maximum power, a liability which also contributes to high emissions.

One solution that has been proposed is to manufacture the block out of low thermal conductivity ceramics rather than metal. Ultrahard Materials of Great Britain has done some prototyping in this area but has not secured the funding to proceed with the project. Freedom Motors of Davis, California has taken the halfway approach of coating the combustion chamber with a fine ceramic while retaining structural aluminum for the rest.

Freedom Motors claims substantially better fuel economy than ordinary spark ignition reciprocating engines of equivalent horsepower and vastly lower emissions than other Wankels, claims that have not been entirely substantiated by third parties. Freedom Motors has produced many prototypes but is not in the production business and is seeking to license the design. Many companies are currently evaluating the design, and one company, Rotapower, is actually making engines. Whether the engine will succeed in the marketplace is still uncertain.

Various other Wankel designers are active around the world, most in the area of general aviation where the high power density of the engines is highly advantageous. Wankel Gmbh of Germany and Mid West Motors of Great Britain both make innovative Wankels, but neither has achieved great success in the market nor has either managed to achieve any real efficiency breakthrough.

We believe that Wankels will continue to fascinate mechanical engineers and that new versions will continue to be developed, but we believe that the inherent limitations of the design will probably prevent any significantly greater market penetration than has already been achieved. Those who require the extremely high power to weight ratios afforded by the Wankel will continue to buy the engine, but the piston ICE will remain overwhelmingly dominant.

Notwithstanding the Wankel’s indifferent success in the market, numbers of innovators have attempted to promote other rotary designs. Two of the most interesting are the Quasiturbine and Phoenix Navigation Tesla Turbine.

The Quasiturbine is the brain child of an exnuclear physicist named Giles St. Hilaire who resides in Quebec. The design has received a great of attention from the automotive press and has excited considerable controversy.

Utilizing an ellipsoidal housing reminiscent of the Wankel, the Quasiturbine substitutes a deformable four faced rotor for the Wankel’s eccentrically rotating triangular piston. The four faces of the Quasiturbine rotor provide more power strokes per revolution than is the case with the Wankel’s, and the flexible structure of the rotor appears to ameliorate the sealing problems associated with Wankels. The rotor also works in a purely rotational fashion unlike that of the Wankel which reciprocates as it turns, and thus vibration levels of the Quasiturbine should be very low, comparable to those of a Brayton turbine. St. Hilaire claims very high efficiency for the design as well, and that claim rests upon a further claim that seems on the face of it rather incredible. The further claim is that the Quasiturbine operates successfully in the pulse detonation mode.

In the normal course of things, one would expect the Quasiturbine to exhibit the same thermodynamic deficiencies as the Wankel, namely severe loss of thermal energy through the engine walls and incomplete fuel combustion. Nevetheless, if St. Hilaire’s claims are really true, the increment in overall efficiency brought about by pulse detonation should more than make up for any thermal losses.

To date those claims have not been independently verified. St. Hilaire in his technical literature indicates that pulse detonation once achieved continues indefinitely as fuel is added to the engine, but since pulse detonation is supersonic, that would appear to require a very high engine speed if it in fact were true. The other problem is initiating pulse detonation. Most attempts to do so have involved supplementary combustion chambers and complex arrangements of internal baffles, which are possible in a turbine with a combustion chamber of fixed dimensions but not in a Quasiturbine where the dimensions of the chamber are constantly changing.

Also claiming success in achieving pulse detonation in a rotary ICE is Ken Rieli, president of Phoenix Navigation. Rieli’s innovation is based on the famous Tesla or boundary layer turbine developed by the great Nicola Tesla in the late nineteenth century and unsuccessfully promoted by the latter in the twentieth century.

The Tesla turbine is simplicity itself, consisting of a combustion chamber housing a number of thin, closely spased discs attached to a spindle. A jet of burning material is directed into the chamber parallel to discs and the viscous drag of the gas on metal surfaces causes them to turn. The gases are exhausted through holes near the center of the discs.

There’s no question that Tesla turbines work. Tesla himself demonstrated working models a hundred years ago. The main problem was that the overall conversion efficiency was extremely low—no more than a few percent.

Recently, some academicians have theorized that Tesla efficiency could be improved to approximately the 30% level—equivalent to that of an optimized Brayton—and a couple of startups apart from Phoneix have attempted to sell improved designs. But Phoenix claims forty not thirty percent and the claim rests upon the much higher efficiencies to be had from pulse detonation.

Is there anything to the claim? We don’t know. I have interviewed Rieli, who clearly has an extensive background in mechanical engineering and who certainly talks the talk, but he did not disclose how pulse detonation is achieved in his design nor how the associated problems of noise and vibration are minimized.

In truth, Rieli faces the same problem of most ICE innovators today, attempting to compete with entrenched and proven technologies whose supporters are immensely rich and powerful concerns. His company does not produce production engines, only prototypes and kits for experimenters, the common lot of most engine innovators today.

Even with a simplified design such as the Tesla, the costs of small production runs and custom fabrication are extremely high and tend to make the products noncompetitive. In order to price the product competitively the manufacturer simply has to acquire his or her own tooling, which in turn requires massive investment, probably in the eight figures. For this reason many of the innovators who actually make production models utilize more conventional designs that permit them to use a lot of stock parts. What this means ultimately is that any successful ICE innovation is likely to be a piston not a rotary engine.

In the following section we’ll look at a number of highly innovative piston designs and conclude this series of tutorials.