Steam/Electric Hybrid Car Design
The diesel electric train replaced the steam locomotive, the navy uses steam to run electric engines. Ever drive an electric golf cart? They have really good torque at low speed. Try driving a gas powered car or golf cart over a curb at low speed. An electric drives right over.
I would love to convert something like a GEO Metro car to steam/electric but this is beyond the scope of cottage industry.
Steam engines are simple but using them to power a car raises all sorts of issues. Governing steam boiler output at low demand and high demand requires a demanding control system. To provide enough power to drive a car at speed requires the use of a high pressure high temp system.
To power a steam engine at a constant speed is much less demanding and the system can be purpose built for this speed. That is suitable for a generator which likes a constant speed.
Cars require no power input when stopped or coasting. They require maximum power when accelerating hard and when over speeds of 55mph when wind resistance becomes the major factor.
Between those extremes a car requires varying amounts of power input.
Electric cars require a large load of batteries to attain speed and range. That load imposes a weight penalty further drawing power and range. Its a delicate compromise.
Current hybrids on the market are kind of a gimmick. The public demanded them and they are being served up. In most, the electric power only assists the meager IC engine in accelerating. In the middle of the HP curves the IC engine is sufficient, but needs the boost from the electric motor to get going. This allows for more fuel efficient gearing and lower rpms. With the Prius the engine actually stops running when there is no demand, which is why it can get better mileage in town than on the freeway.
It is proposed here to make a car driven by an electric motor, that carries a light load of batteries of say 96 volts. These batteries are charged by a continuous duty steam engine generator system. At stops and while coasting the batteries are being charged. At speed the electric motor will draw down the batteries over and above what the steam generator can output. So range will again be a compromise between the size of the steam generator system and the weight of the car.
A normal IC powered car has an exhaust system comprised of a manifold, pipe, catalytic converter, resonator and muffler. Imagine in this same space a combustion chamber, steam coil, evaporation coil and preheat coil. From the boiler to the preheat coil the above components will span the length of the cars underbody. Within the normal section of the exhaust pipe would be a bundle of six 3/8" copper tubes conducting preheated water to the evaporation zone. So utilizing the entire length of the car gives a large boiler surface area without filling the under hood area.
Under the hood you would find an electric motor direct coupled to the transmission, a final stage burner/boiler with its controls, steam engine/ generator, and battery bank.
The electric motor seldom needs servicing except for brushes.
What's the big advantage? Electric motors are very efficient, steam engines running at constant speed are very efficient and clean burning. Fuels for a steam engine are very flexible, diesel, gasoline, propane, bio are all good candidates.
What HP for the hybrid? 20 - 40Hp would be sufficient for constant driving around town with a 2000 lb. compact car and with a good range on freeway. Remember that steam engines unlike IC engines put out a better torque curve at all rpm. A small steam engine can put out as much power as a larger IC engine.
What kind of mileage? The biggest robber of fuel is wind resistance, rolling resistance and heat and friction losses. A normal IC engine dumps a tremendous amount of energy as wasted heat out the radiator. A steam engine converts up to 80% of the heat to power. Wind and Rolling resistance have to be dealt with through aerodynamics and weight to strength ratios.
What burner? Espar - makers of truck heaters www.espar.com/html/products/hydronic10.html makes a nice unit that burns gasoline or diesel and is extremely efficient. I have converted these to fire a monotube boiler. They have ignition switch or push button start, with safety shutdown modes in case of no fireup or over-temp, and they have a three speed cycle for low to high output which can be governed by steam pressure.
Upon starting the proposed steam electric hybrid, the car can move off immediately with its electric motor, the boiler burner automatically fires and as soon as steam is raised the steam engine is started by a small electric starter. The steam generator continues running so long as the batteries need charged or until the car is switched off. A short and efficient cutoff can be used for the steam engine with no need need for variable cutoff or compounding high pressure steam.
I would propose 250 psi and about 425 F steam running a simple expansion rotary steam engine. This engine has no compression cycle and can be made quite small and about the size and dimension of the generator. The two can be unitized into a unit 12" diameter by 20" long.
Not all the parts are shown here. There is a virtual cylinder head that rotates as the piston circles around. The piston is a wiper plate bushed with teflon. It is 4" long and 1.5" deep. The piston chases already expanded steam out the exhaust port on its way around. The shaft and rotor end plate are not shown in this photo.
I would love to hear your thoughts and suggestions.
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