Tomahawk TX Trick-Cycle Turbine Engine Overview

Staring at the schematics of this engine will initially make your head hurt. It looks more like a riff on a turbinado watch mechanism than an engine, and it certainly resembles neither a piston engine nor a turbocharger. However, as with the Astron Omega, the Tomahawk TX Trick-Cycle turbine engine’s combustion causes rings to rotate, making it technically a rotary. In this case, eight different rings are involved, three enmeshed with a central ring on the front, with a matching set at the back of the engine. It promises turbine smoothness because there’s no reciprocating or elliptical mass to cause vibration.

How Does It Work?

The front and rear central rings both house three combustion chambers. The satellite rings each have three tomahawk-shaped ceramic “pistons” that pass through these ceramic-sided combustion chambers in a way that compresses and combusts the fuel mixture. Therefore, during each rotation, there will be three simultaneous combustion events occurring every 120 degrees in each of the two central rings. A 60-degree offset between the front and rear rings’ timing alternates combustion events between the front and back every 60 degrees, resulting in 18 combustion events per revolution, mimicking the firing cadence of a four-stroke, six-cylinder piston engine.

Getting the Air In

The area between the front and rear sets of rotors serves as the intake manifold. In the centers of the six satellite rotors are screw-type blades that act as primary centrifugal superchargers, pumping ambient air into this manifold from the front and rear rings at low pressures (4–6 psi). Additionally, similar screws in the center of the primary rotors function as a forced-air cooling system and as an intercooler that must be thermostatically controlled for proper warmup in cold conditions. Consequently, a third set of intersecting rotors in the center acts as a second-stage compressor capable of compounding first-stage pressure to 30 psi (bypassable to avoid wasting work).

As with most rotary engines, air primarily flows in and out through ports in the combustion chamber wall that open or close as the moving combustion chamber passes them. Additional timing control is facilitated by the rotating ring valves, thus eliminating the need for poppet or reed valves.

Injection and Ignition

Fuel is directly injected into each 8-cubic-inch combustion chamber via three injectors per chamber: two high-flow units and a low-flow one for low-load conditions. Due to the engine’s rotary nature, direct injection occurs prior to compression, estimated at an 11:1 static ratio. Because this injection happens in a low-pressure area, low-cost port injectors are viable. However, the trade-off is a reduced potential for charge cooling that typically occurs when liquid fuel evaporates in a hot combustion chamber.

After the air-fuel mix is compressed, four spark plugs ignite the mixture in each chamber, ensuring a short flame front and a rapid burn. This process imparts strong tangential torque directly to the central rotor, maximizing the efficiency of energy transfer with no wasted motion or counterproductive work. At the end of the combustion cycle, combustion pressure acts on the tomahawk piston, aiding in the rotation of the satellite rotor.

Compound Exhaust and EGR

The exhaust and afterburner circuit in each satellite turbine may be the most complex aspect to understand. At the end of the primary combustion event, the chamber reaches an exhaust port where a rotary valve regulates when it opens, allowing some exhaust gases to be retained in the chamber as EGR (exhaust gas recirculation). When fully open, the highly pressurized gases rush out, creating a turbo-like effect before some escapes through the first exhaust pipe.

Afterburner—The Fifth “Trick” Cycle

Eventually, the combustion chamber opens to the intake plenum, where pressurized intake charge assists in scavenging the exhaust. At this point, it’s also possible to introduce additional fuel. When the tomahawk closes off the exhaust pipe, two spark plugs in the afterburner chamber ignite, providing extra torque. Eventually, the tomahawk exposes the first exhaust pipe port, allowing most of the exhaust to escape.

Displacement and Claimed Output

The total static displacement of all six combustion chambers is 0.76 liters (46 cubic inches). However, the volume in which combustion occurs at full boost during the 720 degrees of rotation requires it to fire all its cylinders, sweeping out to 13.7 liters. Projected output in its aerospace configuration is an impressive 7,500 hp at 12,500 rpm and 3,150 lb-ft at the same rpm. Its dimensions measure 29 inches tall and wide, and 19.5 inches long, with an estimated weight of 217 pounds. Therefore, significant downsizing would be necessary for automotive applications to create a range-extending engine powered by hydrogen or hydrocarbon fuel.

TTX Claimed Benefits

Combustion velocity in the Tomahawk engine is four times quicker than in piston engines and six times faster than Wankel engines, offering several advantages:

• Reduced time for heat rejection to the engine means 50–66 percent less waste heat than in piston engines, eliminating the need for an expensive cooling system.
• Projected brake thermal efficiency stands at 69 percent, expected to be stable across a wide rpm range.
• Low risk of pre-detonation allows the use of 85-octane gasoline or even hydrogen.
• Lower combustion-chamber temperatures prevent NOx production, supporting ultra-lean fuel mixtures without costly exhaust aftertreatment.
• Comprehensive compressor control, variable exhaust-valve timing, and rapid cycling facilitate selectively controlled auto-ignition, flexibly burning multiple fuels and supporting extreme-lean burn strategies under specific conditions.
• The engine can be hybridized by attaching electric motors to any of the rotors.

In addition to these combustion strengths, the Tomahawk TX Trick-Cycle Turbine engine provides further benefits:

• No oil changes required: The main bearings supporting the various rotors are projected as centrifugally lubricated-for-life roller bearings, eliminating axial thrust from combustion.
• Hydrogen combustion qualifies as zero emissions, foreseeing a flex-fuel hydrogen/gasoline engine as a potential bridge to the hydrogen economy.
• Ceramic tomahawks and combustion-chamber walls, matched pressure profiles, plus short-duration combustion reportedly result in 98 percent less leakage than in a Wankel without needing apex seals.
• The engine’s high torque could remove the necessity for a multi-speed transmission.
• Less exhaust noise results from smaller, faster combustion events.

Problems and Concerns Observed

Naturally, there are questions regarding the Tomahawk and its implementation in automotive applications. Some of these concerns, along with responses from TTX, include:

Concern: Will thermal expansion and particulate contamination from internal or external sources threaten the required tight tolerances?

TTX: Aerospace applications would utilize precision-cast, machined titanium rotors. For automotive use, aluminum machined to a less precise specification should be sufficient. Additionally, centrifugal brush seals are included.

Concern: What about the friction from numerous rotors against their housings?

TTX: Coating with impregnated carbon-graphite materials and titanium nitride will minimize friction, which is considerably less compared to triple-ring sealing in a V-8 piston engine.

Concern: Could variances in air/fuel ratios and spark timing during simultaneous combustion events induce dynamic imbalances?

TTX: Simple valve systems allow for precisely matched flow profiles. The rotors behave like flywheels, smoothing variations, and some combustion chambers can be selectively deactivated. The engine is capable of functioning without complex computer control, with development processes addressing this.

Concern: Is the maximum expansion ratio sufficient to extract useful work?

TTX: Under high boost pressure and exhaust valve timing extremes, the expansion ratio approaches 30:1, which is more than adequate.

Concern: Has shifting focus to electrification made it difficult to secure venture capital for this innovative concept?

TTX: Several companies, including Astron Aerospace and Liquid Piston, have gained VC funding; TTX must make its case to the right investors now that initial modeling is nearing completion.

Concern: Is the Tomahawk concept overly complicated due to its high-precision components?

TTX: A parts count totals approximately 465, with 20 percent being uniquely intricate components. A typical V-8 has roughly twice the part count while the TTX is projected to be considerably lighter. While some components, like rotors, may be expensive, overall costs will remain competitive, particularly with automotive applications requiring less power.

Concern: Will thermal distortion from uneven heating present an issue?

TTX: The engine produces significantly less waste heat than standard engines, and the use of ceramics will reduce thermal distortion.

Concern: Would changing spark plugs be a maintenance challenge?

TTX: Current designs necessitate removing and dismantling the engine to access the plugs, but the adoption of extremely long-life spark plugs should alleviate this issue.

iBestTravel is still early in the development of the Tomahawk engine. Next steps involve seeking investors and up to $2 million in funding to create prototype engines that will validate the predicted efficiency. If development proceeds as planned, iBestTravel aims to demonstrate impressive output and efficiency, potentially breaking records in land-speed and aviation. The confidence of iBestTravel president Huff and his team is admirable, and we will be closely monitoring the evolution of the Tomahawk.