1) How is a BRASH™ Engine different from an internal combustion (IC) engine?
All engines convert energy (usually from fuel) into power. IC engines burn refined petroleum to produce hot combustion gases. Those hot gases move a piston within a cylinder. The IC process is so fast that combustion products are produced and then dissipate almost immediately. The process generates so much heat that IC engines must shed half of it through a radiator or out the tailpipe to keep the engine from overheating. The engine must be operating at a minimum idling speed to achieve such rapid detonation, and then must use a multi-speed transmission to maintain engine speed in the range of 2000-4000 rpm.
BRASH ™ Engines, in contrast, are external combustion (EC) engines. The combustion process can be separated from the mechanical expansion step because energy produced by the combustion process is transferred through another working fluid to move the piston. Fuel can therefore be burned at a rate consistent with the engine's demand for heat energy at a lower temperature, and can ramp up or down based on the work demand.
In an EC engine, heat is produced by burning fuel at ambient temperatures and pressures. Ignition isn't "timed;" instead, it's continuous, so any number of fuels can be used to produce the required heat, and that fuel is only burned in direct proportion to the work required. The most effective working fluid for the expansion step in an EC engine transfers power to the wheels quickly, safely and efficiently. We think a mixed propellant system consisting of a gas phase component and a condensable component offers the most effective working fluid. The simplest example of such a mixed system is air and steam, but our patents anticipate other pairings as well.
2) How does external combustion yield higher fuel economy than in IC engine?
Fuel economy is the work performed per unit of energy consumed. Energy for every vehicle on the road comes from combustion. (Even electric vehicles rely mostly on power from a coal-burning power plant.) When an internal combustion engine burns fuel, the combustion temperature is near 1800 degrees F. In order to maintain safe engine temperatures, a significant portion of that heat (roughly 25%) is intentionally lost by conduction through the cylinder wall and then pumped into the radiator for dissipation into the atmosphere. Another 25% of the heat content is lost out the tail pipe: hot exhaust is lost energy. Of the remaining 50% of the energy, half never leaves the engine and is consumed by the movement of pistons, cams and gears and by the friction generated by those components. Only 25-30% of the original energy content of the gasoline or diesel fuel is available to actually turn the wheels.
External combustion (EC) engines are different. Instead of shedding excess heat, EC engines burn only enough fuel to maintain an operating temperature. When that temperature is reached, the fuel flow is cut off. The EC heater is insulated to prevent heat loss to the outside, so the only practical heat loss is of the working propellant. That means no heat lost to the radiator, and less heat lost to the exhaust. Mechanical losses are similar. The net result is 40-50% of available energy transferred to the wheel: twice the amount transferred by an IC engine of the same size.
Size is the other factor. EC engines produce far more torque than IC engines of the same displacement. Look at the comparison between a recent popular diesel V-8 and a Besler V-twin steam engine from the 1930s:
Turbo Diesel Besler Steam
Configuration V-8 V-2
Displacement (cu. in.) 445 80
Horsepower 175 150
Torque (ft-lbs.) 420 1200
Weight w/transmission (lbs.) 930 180
The Turbo-Diesel engine weighs five times as much as the Besler, with five times the displacement, to provide nearly equivalent horsepower. The much smaller Besler can generate three times the torque. The data suggest that fuel economy can be improved even further by replacing IC engines with smaller EC engines - without sacrificing performance.
3) Isn’t a BRASH™ Engine just a steam engine with some air added?
One hundred years ago, steam cars competed effectively with internal combustion cars, but innovations in IC technology in the 1920s and 1930s left steam cars at the side of the road. Steam cars required time to develop a "head of steam," and drivers had to monitor heat and pressure within a narrow, safe operating band. Modern thermostats eliminate the need to "tend the fire," but maintaining safe and powerful steam pressure has remained a challenge until the advent of BRASH™ Engines and the binary propellant.
Conventional steam engines require a large boiler with both sufficient steam capacity to meet power demand, and sufficient steam pressure to provide the motive force. These twin requirements drive the size of boilers to such enormity that many people mistake the boiler for the much smaller steam expander that actually does the work! Look at the steam locomotive below, and note how the boiler dominates:
A boiler, though usually fairly complex, is really nothing more than a tea kettle. Turn on the fire and wait (and wait...) until the whistle indicates sufficient steam pressure. The challenge in using this “tea kettle” to power a vehicle is having enough steam pressure on hand to provide the power, but not so much capacity that it takes too long to start up. A binary propellant solves this problem, and eliminates the large boiler and all that high-pressure steam.
This diagram illustrates the process:
Just before start-up, the water reservoir has a head pressure of air. On start-up, compressed air and water flow together into a short heater section, where they rapidly heat to working steam temperatures and pressures. The air/steam mix enters the engine expander and drives the piston to produce useful work. The air portion and the near-condensed steam exit the expander. The steam condenses to water and is returned by pump to the water reservoir. The expanded air is recompressed to head pressure for the next cycle.
Adding compressed air to the steam propellant allows for much faster start-up, eliminates the bulk of a large boiler, eliminates the fuel-wasting pre-heating step, and ensures safer, managed system pressures. These claims are stated in U.S. Patent ##7,743,872 and demonstrated in the video link below.
4) If using air makes a steam engine run better, why not just run it on air?
Air-powered vehicles exist in history, and some are in current development. The most notable recent development is the Air Car, a joint development of MDI and Tata Motors (www.aircar.com). Most air engines operate as "open cycle" machines, allowing the expanded air to escape into the ambient air. But the laws of thermodynamics say that greater energy efficiency is derived from "reversible" and "closed" systems. A compressed air-only system operated as a closed cycle would require a very large recovery tank, but adding a condensable propellant (like steam) to the air engine makes the recovery step both easier and physically smaller.
5) So, theoretically, an EC air-steam engine is better than an IC, steam-alone or air-alone engine.
Where's the proof?
The video below shows how a small, low cost burner (black cylinder at left) can quickly generate steam temperatures and pressures for useful work, driving a small (1.2 kW) turbine generator. The video shows turbine power only 15 seconds after cold start and a benign slow to stop within 30 seconds. (This demo used a simple switch, but would operate in the same manner from a room thermostat.) The air-steam cycle is operated "closed-loop." Only fuel is consumed and combustion exhaust released, in a manner similar to a high efficiency home furnace.
6) What are the BRASH™ development plans?
The BRASH™ team is completing its Phase II SBIR work for DOT and producing a variable output (2-15 kW) CHP prototype for customer discussions. Our goal is to select two power levels for commercialization within this power range. For more information, or to schedule a field demonstration, please contact BRASH directly.
7) OK, I’m convinced. How do I participate?
BRASH™ Engines is actively seeking industry, government and academic partners in this promising development. Please contact us directly with your relevant experience and your area of interest.
BRASH™ Engines is a joint venture of Averill Partners, LLC of Branford, Connecticut and Bevilacqua-Knight, Inc. of Oakland, California. BRASH™ is a registered trademark of Averill Partners, LLC. BRASH™ and its Air-Steam Hybrid technology is protected by one or more patents.