Otto or Rankine Cycle ~ Which Is Better?

Ever since engines were installed in carriages there has been an ongoing discussion among automotive enthusiasts about the merits of the steam engine (Rankine cycle) powered carriage over the internal combustion engine (Otto cycle) powered carriage. At the end of the 1800s the steam engine reigned supreme as the state-of-the-art power plant. It wasn’t until the early 1900s that the internal combustion engine (in its various derivatives ~ two-cycle, four-cycle, diesel) became the engine of choice for delivering power to an assorted array of applications. While steam engines were the early choice to propel self-powered carriages, by the time the name had changed to “automobiles” the engine of choice had changed to the four-cycle internal combustion engine.

Listed below are the various arguments often cited that favor one engine design over the other. The arguments below are gathered from the literature and advertising of the early 1900s. The focus is the Stanley steam car with respect to a generic internal combustion powered car. As such, some arguments are still applicable today even considering the decades of technological advances made to the internal combustion engine. Other arguments for the steam engine are less relevant today due to technological advances made to the internal combustion engine. It is interesting to wonder if given the same amount of time, effort, and expense for technological evolution and advancement, would the steam engine of the 21st century have been the better choice long term as the power source for our modern automobile.

The comparisons below are related to a four-cycle internal combustion engine which was the steam engine’s main competitor in the early 1900s. The comparisons are not applicable to the two-cycle internal combustion engine or the diesel internal combustion engine as compared to the steam engine (although many will be true in these comparisons as well). The reader is advised to couch each of the arguments listed in the background of the technology of the early 1900s. The comparisons are in no particular order of importance and it is for the reader to decide the relative merit of the comparison. The comparisons below only reflect on the engines and do not include arguments related to the physical driving of the vehicle.

Steam Engine Advantages Over The Internal Combustion Engine
1.	There are far less moving and/or sliding parts in a steam engine then in an internal combustion engine. A simple steam engine can has as few as 13 moving parts while an internal combustion engine as many, many, more. When the clutch and transmission is added in the steam engine is clearly a simpler engine.
2.	A two-cylinder steam engine delivers as many power impulses to its crankshaft as an eight-cylinder internal combustion engine. In two revolutions of the crankshaft, a two-cylinder steam engine delivers eight power impulses; the same as an eight-cylinder internal combustion engine.
3.	A steam engine is self-starting. An internal combustion engine can not start itself and requires a means to get it going (an electric motor of several horsepower rating). The starting mechanism (and associated battery, generator to recharge the battery, and wiring) then becomes dead weight that must be carried with the engine while it operates.
4.	A steam engine can be stopped at will thus no clutch mechanism is required between the steam engine’s crankshaft and what the steam engine powers. The only reason for a clutch (or equivalent) on an internal combustion engine powered vehicle is that the vehicle must be able to be stopped while the internal combustion engine continues to run at low power output levels.
5.	The steam engine can efficiently deliver power at very low crankshaft speeds as well as up through the maximum crankshaft speed. For a steam engine the fuel efficiency is determined by the burner heating the boiler and thus the consumption of fuel can be optimized. At low crankshaft speeds (less than 1,000 RPM) the power available from an internal combustion engine is marginal and not an efficient use of the fuel being consumed (fuel is being consumed just keeping the engine running). The internal combustion engine only becomes fuel efficient at higher crankshaft operating speeds.
6.	Steam engines develop maximum torque with their crankshaft at standstill thus power is available when it is needed most ~ getting what the engine powers going or moving initially. The internal combustion engine only develops maximum (torque) at high revolutions of the crankshaft which requires clutches and transmissions in order to provide high torque at low speeds of the output.
7.	Stanleys have no transmissions as the engine is directly geared to the rear axle. Transmissions used with internal combustion engines (even those of today’s cars) generate perceptible variations when changing gear ratios.
8.	There is virtually no vibration with a steam engine. Power impulses are delivered uniformly and as a continuous “push” by the pistons. Internal combustion engines (or internal explosion engines as the Stanley twins called them) rely on a violent explosion on one side of the piston to deliver a power impulse. The explosions rock the whole engine and must be damped out by mounting arrangements. The internal combustion engine’s pistons are “hammered” by the explosions necessary to create the engine’s power where as the steam engine’s pistons are pushed by the forces of steam acting on either side of them.
9.	The steam engine is a low-speed engine thus wear of mechanical parts is greatly diminished. A Stanley steam engine turns at 300 to 400 RPM to maintain a 35 MPH speed (depending on tire diameter). The internal combustion engine must run at 600 RPM or higher just to continue running at “idle”. Internal combustion engines operate at 1,500 to 2,500 RPM when the vehicle is moving along at 40 to 50 MPH (again depending on tire size and transmission gear ratios).
10.	The cylinder explosions of an internal combustion engine must be muffled by a labyrinth of baffles and porting to quell the noise from the exhaust ports; all dead weight that the engine must carry along. The steam engine has a relatively noise-free exhaust if vented to atmosphere and no exhaust if the engine is arranged to recover the exhaust steam as condensate.
11.	The steam engine does not require a cooling system. The high temperatures are limited to the boiler which is designed for the application. The cylinders and pistons are only exposed to the heat of the steam which is in the 600° to 700° Fahrenheit range (for a 600 PSIG boiler operating pressure). The explosions of an internal combustion engine generate high temperatures that can damage the metal cylinders and pistons if proper cooling is not continuously provided. The cooling system is added weight for the engine block.
12.	All of the power developed by a steam engine’s pistons (except a minor amount required for moving the valve train and overcoming bearing friction) goes to turning the crankshaft. A steam engine’s pistons are powered by steam pressure from one end of the cylinder to the other and back again and except for friction there are little losses. The internal combustion engine’s pistons are only powered from one end of the cylinder to the other (during the power cycle) and must be returned back using some of the engine’s developed power. Additionally each internal combustion engine’s piston must act as an air compressor for one of the four end-to-end cycles a piston makes in the cylinder (the compression cycle) further using some of the engine’s developed power. The internal combustion engine’s piston makes a full cycle in the cylinder during the intake and exhaust cycles and thus generates wear, frictional losses, and consumes additional power the engine could supply to the crankshaft in moving internal mass back and forth in the cylinder.
13.	A steam engine does not require a flywheel to dampen out the engine’s power impulses and vibrations. Internal combustion engines include a flywheel on the crankshaft to smooth out the power impulses applied by the pistons to the crankshaft and to assist in maintaining the rotation of the crankshaft through three end-to-end cylinder strokes of each piston when no power is being generated by each piston.
14.	When you stop a steam engine driven vehicle you stop the engine. All engine wear ceases. When you stop an internal combustion powered vehicle the engine continues to operate at a low RPM. Which you can shut down the internal combustion engine, it must be restarted before the vehicle can move again. The steam engine when stopped is instantly ready to start (provided adequate steam pressure still exists).
15.	When you stop a steam engine driven vehicle the combustion process at the boiler continues for a short time until the boiler pressures stabilize and then combustion continues sporadically. When an internal combustion engine driven vehicle is stopped the engine continues to operate and consume fuel unless it is shut down and then restarted.
16.	A steam engine with a vaporizing burner (a burner arrangement where liquid fuel is heated to a vapor and the vapor is consumed) fired boiler arrangement will burn nearly any liquid fuel; gasoline, kerosene, diesel fuel, fuel oil, aviation (jet) fuel, etc. No additives or other modifications to the fuel supply are required. The internal combustion engine is a single fuel engine and that fuel must be refined to a tight set of requirements. Additionally the fuel for an internal combustion engine requires additives to improve combustion and eliminate knocking (tetraethyl lead was the additive).
17.	The steam engine does not require an electrical system for operation. A means to ignite the compressed fuel mixture of an internal combustion engine is required (either with a magneto or generator, battery, and ignition coil).
18.	The steam engine crankshaft is easily reversed (through the simple change of position of a valve link). The internal combustion engine’s crankshaft will only rotate in a given direction and requires an external gear change (transmission) to reverse the rotation of the output shaft.
19.	Lubrication of the steam engine is simpler. The steam engine carries oil in the crankshaft enclosure that is splashed about by the rotation of the crankshaft through the oil. This oil is only moderately heated and rarely has to be replaced as it does not come in contact with the combustion process or other contaminants. The steam engine’s pistons and valves are lubricated by adding a minute amount of oil to the steam supply to the engine. The internal combustion engine relies on a labyrinth of oil passages and ports through out the engine to deliver oil to all moving surfaces and the oil is generally only good for a few thousand miles before it has to be replaced due to contamination and other factors. An argument against the steam engine is that oil used to lubricate the cylinders, pistons and valves is lost out the exhaust and thus wasteful (today’s technologies now allow for the removal of the steam cylinder oil from the exhaust steam).
20.	In order for an internal combustion engine to operate properly an intricate set of events, all timed properly, is required to occur in the proper sequence. In addition the air-fuel ratio and spark intensity must be within a narrow band of acceptable performance if the internal combustion engine is to operate efficiently. The burner that heats water into steam for the steam engine is more tolerant over a larger range of air-fuel mixture ratios and a single ignition is required to initially light the burner's pilot. The only timed event associated with a steam engine is the movement of the D-slide or piston valves which admit steam to one side of a piston while exhausting the opposite side.

Its A Draw Between The Steam Engine And The Internal Combustion Engine
1.	Weight is nearly the same for both engines. The steam engine along with its water tank, water pumps, feed water heater, boiler, condenser, fuel tank, fuel pump, burner, oil tank, oil pump, and associated piping is probably equivalent to the internal combustion engine with its radiator, water pump, fuel tank, fuel pump, carburetion, spark ignition, generator/alternator, oil sump, oil pump, battery, starter, and associated electrical wiring and piping
2.	The steam engine is a “stored power” engine. Power is generated externally to the engine (with steam pressure in a boiler) and stored for use by the engine when needed (similar to a battery, generator/alternator, and electric motor). The internal combustion engine is an “on demand” power engine where the power required is generated when it is needed. The disadvantage to the steam engine is that the power must be generated and stored before it can be used. The disadvantage to the internal combustion engine is that it always is generating power which is wasted during short periods when no power is needed.
3.	Both engines require a fuel system involving pumps and pressure regulation devices. Early Stanley cars were single fuel where as later cars (for safety concerns) were two-fuel cars. The use of two fuels involves additional components and thus can be considered a negative point for the steam engine powered car. The Doble steam car burner technology returned to a single liquid fuel source (the Doble burner is the basis for all home fuel oil heating systems used today).
4.	Both engines use a radiator/condenser. The steam engine, to be more efficient, needs to reuse its water supply which involves cooling the exhausted steam back to condensate/water through the use of a condenser. The internal combustion engine requires a radiator to maintain the engine cooling water at the proper temperatures.
5.	Neither engine is highly efficient. Both engines consume a liquid fuel and generate a high quantity of heat which is lost and not able to be converted to useful work. Both engine systems (in the early 1900s) provided about the same fuel economy in miles per gallon of fuel consumed.

Have an idea or suggestion that should be included in the above discussion?
Please email me with your thoughts.

Internal Combustion Engine Advantages Over The Steam Engine
1.	The internal combustion engine can be started immediately from a cold state (provided the support electrical system, fuel system, ignition system, carburetion system are adequate) and deliver power to its load. The steam engine (even when used with a flash boiler) requires a short delay before the engine can deliver power (but once the boiler is hot is like the internal combustion engine in that it delivers power instantly).
2.	The internal combustion engine develops high output shaft speeds naturally (a benefit for powering aircraft or boat propellers for example). The steam engine needs a gear change to develop high output shaft speeds).
3.	Water freezes. Anti-freeze can be used with an internal combustion engine’s cooling system. The boiler, water tank, water lines, and even the steam lines (since they contained condensate) associated with the steam engine must be protected and not allowed to freeze.
4.	The internal combustion engine, because once started it is always running, is better suited to continuously power auxiliary pumps, generators/alternators, and similar hardware. Because steam engines may be stopped easily by removing the steam supply, any auxiliary hardware requiring continuous power input is required to have an alternate power source (electric motor, steam turbine, etc.).
5.	Under an emergency there's no stored energy to release with an internal combustion engine. The water in the boiler supplying a steam engine has a great amount of stored heat energy that must be dissipated or at least dealt with in the event of an emergency.

Stanley Philosophy and Beliefs
1.	The Stanley twins did not believe in an economy of consumption thus the cars were built to last “forever”. Aluminum car bodies don’t rust and are lightweight. You only needed mass production if you intended on making a disposable vehicle.
2.	No guarantees or warranties were offered with their cars. The Stanley twins were men of the highest integrity and word and if their product were defective they would make it right (as long as it was their fault and not normal wear or abuse). As no written guarantee or warranty was provided with a new car purchase, it was considered insulting to ask them to guarantee or warranty their product in writing.
3.	The Stanleys were not style or fad conscious. Changing a body style or just to keep in style or to display wealth or privilege was not their way. The steam carriage was intended to be a thrifty, practical, economical mode of transportation and not a fashion statement nor an indication of one's success in life.
4.	The Stanley twins did not believe in credit. A customer ordered their car generally from a catalog of pictures and specifications; the Stanleys built their car for them in good faith; and the customer was expected to pick it up in a prompt and timely manner and pay for the car in full, in cash.
5.	There was little advertising for their cars. They considered money spent on advertising a waste of valuable resources and better used improving their product. The Stanley twins believed they built a superior product and that word-of-mouth praise for their cars would sell more.