The Engine of the Future

The CEI/SED Variable Compression Ratio, Low Friction, Lean Burn Engine

Albert E. Sanderson, Ph.D., Sanderson Engine Development, LLC
Michael A.V. Ward, Ph.D., Combustion Electromagnetics, Inc.

The ideal, practical, highest efficiency internal combustion engine is one that operates on what is known as the Otto cycle, with highest compression ration (CR), leanest air-fuel ratio (AFR), fastest burn, and lowest frictional losses, both air-throttling and piston rubbing. Such an engine is also the cleanest engine as long as it can use a homogenous air-fuel mixture, as in a gasoline engine, so that, at light engine loads, it can operate as a lean burn, fast burn, high CR engine with low inherent exhaust emissions, and at high loads, it can operate with a stoichiometric mixture for best power and best use of the 3-way catalyst for lowest tailpipe emissions. With the addition of an integrated hybrid feature, also known as a mild hybrid, not to be confused with the highly complex and expensive conventional hybrids (either gasoline or diesel electric), it can double gas mileage with the lowest possible emissions.

Such a gasoline engine has been considered an idealization, abandoned by the auto industry as too difficult a challenge, which includes abandoning both the lean burn and variable CR low friction aspects of the engine, and the 60 mpg that could be achieved in a vehicle that currently gets 30 mpg. In its place, the gasoline-electric and diesel-electric hybrid and fuel cell technologies are being pushed, which have serious technical flaws and cost problems and will do little, in the near term, to alleviate America's serious energy problems, in terms of its record oil imports and ever increasing vehicle costs.

That can now all change to achieve what was considered only as theoretically possible before, based on major developments made by CEI and SED, who having worked independently of each other, have solved each half of the problem needed to achieve the ideal, but practical, Otto cycle engine mentioned. For CEI, the driving force was Dr. Michael Ward, Ph.D. Harvard University, joined by his thesis advisor, Professor Tai Wu, by Dr. Fred Kern, MIT Ph.D., Engine Lab, and by Robert Lefevre, a leading electronics engineer, who together collaborated to find a practical, low cost solution to lean burn. For SED, it was Bob Sanderson, joined by his brother Dr. Al Sanderson, coincidentally also a Ph.D. graduate of the same Engineering and Applied Physics Division at Harvard as Dr. Ward, who made the breakthroughs to develop the low friction variable CR mechanism that would work ideally with CEI's lean burn developments, to produce the idealized but practical Otto cycle engine.

CEI's realization of lean burn was done in a more effective and lower cost way than was thought possible, resulting in the best of what could be done above the piston, in the engine combustion chamber. Likewise, SED's innovations resulted in the best of what could be done below the piston, in the form of a low cost, low friction, variable CR mechanism. Put together, in the form of a 2-valve, dual ignition engine, we have an engine that is without precedent in its ability to achieve the theoretically highest Otto cycle efficiency with low emissions, at a low cost and simplicity that is worlds apart from the highly questionable diesel-electric hybrids and fuel cell engines.

To add to what had already been achieved to SED's low friction, variable CR mechanism, and to CEI's breakthrough in lean burn, referred to as "The Holy Grail of Car Engineers" by the prestigious Economist magazine, the SED engine naturally allows for the realization of the integrated hybrid, in a hybrid-hydraulic form which provides the most efficient and lowest cost form of regenerative braking, idle stop-start, and acceleration boost required to deal efficiently with the real world drive cycle of stop-starts, and acceleration/deceleration which aggravate tailpipe emissions. With this additional feature, a car that now gets 30 mpg can achieve twice the gas mileage of 60 mpg, and be able to meet the ultra-low emission standards. For SUVs and light trucks, whose mileage could be doubled from the current 20 mpg to 40 mpg, given they now represent over 50% of sales, this could be of paramount importance

In the typical light load city driving of 1/3 load, this engine will be able to operate at a 16:1 CR and 30:1 AFR, with best timing as low as 25º, to achieve a 45% gain in indicated efficiency relative to an engine operating at 9:1 CR, and 15:1 AFR. Add to that the all but eliminated air-throttling and piston friction losses, and the gain in fuel economy (brake efficiency) can be raised up to 70%. Finally, including the integrated hybrid-hydraulic feature natural to the SED engine, gas mileage can be doubled from 30 mpg to 60 mpg with the lowest emissions. Below is a brief description of each half of the system and the results achieved and expected.

In its simplest terms, lean burn is the process of operating an engine with a high ratio of air to fuel, i.e., with lots of air and little fuel, which when properly done, can provide a 30% to 60% gain in fuel economy, depending on the CR. More specifically, to make lean burn work, the engine must be able to: 1) ignite and burn an ultra lean mixture above the 24:1 AFR for low NOx emissions and high efficiency; 2) it must speed up the burn of the normally slow burning lean mixture to achieve close-to-constant volume heat addition for maximum Otto cycle efficiency and low hydrocarbon emissions; and 3) it must burn the mixture in a homogeneous form to avoid any rich hot spots where high NOx is formed, or any overly lean cool spots where high HC is formed. Achieving these three things simultaneously is a requirement for lean burn if best fuel economy and the ultra-low emission standards are to be met. This has not been possible using the conventional ignitions of the past, and the limited conventional ideas of the role of ignition.

Following 25 years of dedicated work and three major technical breakthroughs, CEI was able to develop an ignition/combustion system that could meet the above three requirements, using of all engines, the simplest, lowest cost 2-valve homogenous charge engine. At a CR of 11:1 and an AFR of 25:1, CEI successfully ran a single cylinder, 2-valve engine, with an ignition timing of only 25º BTC, to achieve a part-load efficiency comparable to the Diesel, but without its emissions, weight, size, noise, and cost problems. The lean limit of this engine was 30:1 AFR at a CR of 11:1, and higher than that at higher CR. See SAE paper 2001-01-0548.

Three patented developments led to this success. One was the discovery and implementation of a process called ignition-flow-coupling to produce a torch-like ignition by using a special type of high-energy spark with the purposely generated squish-flow in the engine, to substantially speed up the initial burn (noting that the first 10% of the burn takes 90% of the time). The second development was a revolutionary, coil-per-plug ignition that not only produced the kind of high-energy, flow-resistant spark needed for ignition-flow-coupling, but provides the kind of high-energy-density coil-per-plug ignition sought by the industry, but far superior to what was thought possible. And the third development was the realization that the 2-valve homogeneous charge engine was ideal for this application, since it naturally accommodates two spark plugs and two squish lands for producing the high squish flows needed at the spark plug sites, to speed up the burn of the very lean mixtures, even at relatively low engine speeds where engine in cylinder air-flows are normally low.

Fuel economy gains of 20% to 30% at part load were achieved. However, the CR had to be limited to 11:1 because of engine knock at higher loads. If a practical variable CR mechanism were available, so that the CR could be raised at light load where most of the driving is done, even higher efficiency would be achieved. Ordinarily, the CR could be raised to only 13:1 because beyond that the higher frictional losses and heat transfer losses offset any further gain in efficiency due to the higher CR, as shown by Komatsu (SAE paper). But if lean burn is used with its lower combustion temperatures, and a variable CR mechanism is available with has lower than normal friction, then a higher CR, such as 16:1 may be used. The result would be an increased in indicated efficiency to approximately 45%, (which excludes the greatly reduced frictional air-throttling loss). This large gain is not just due to the increase in CR, but due to the fact that with the CEI combustion chamber, the lean limit would be higher at the higher CR, up to 40:1 AFR, as already demonstrated.

Since the SED variable CR mechanism essentially eliminates the piston sidewall forces, when this advantage is combined with the essentially eliminated air-throttling losses by using lean burn, the fuel economy gain is raised to approximately 70% at light loads, or to 50 mpg from the 30 mpg baseline. Finally, as already mentioned, that mileage gain can reach 100% or 60 mpg, when the SED efficient, integrated hybrid feature is added, i.e., the very efficient, integrated hydraulic-hybrid feature that is inherently built into the engine, as discussed next.
 

In its simplest terms, the Sanderson Mechanism developed by SED is a variable-stroke system for single and multi-cylinder piston engines, using a patented configuration of universal joint and rocker arms to achieve remarkably low friction, small size, and high power-to-weight ratio. Other features are simple variable stroke adjustment, and very low noise and vibration.

The stroke is variable on all pistons simultaneously from a singe point control, easily controlled during engine operation even under all engine operating conditions. This feature is particularly valuable in increasing engine efficiency through higher CR, and reducing emissions, for example during cold-start and other conditions.

The low friction of the Sanderson Mechanism is a result of its rocker mechanism and universal joint drive connection that transfers power from the pistons to the rotating crank. This mechanism is revolutionizing linear to rotary power conversion and rotary to linear conversion in devices such as hydraulic pumps and motors, air compressors and motors and, of course, gasoline engines. The mechanism generates no side load on the pistons to make the power transformation in either direction highly efficient. In both directions the mechanical efficiency is in the high ninety percent range. In gasoline IC engines, this leads immediately to less heat generation, to greater part-load efficiency, and in one test, to the ability to idle without loping to less than three hundred rpm. This leads to better mileage, better acceleration, and less emission when stopped traffic.

Friction is further reduced by the low number of main bearings compared to those in a conventional engine; only three are needed regardless of the number of pistons. The pistons are arranged axially around the main axis of the engine, all driven by their own rocker arms, which share a common U-joint. For greater power to weight ratio, the engine can be double-ended, with two pistons per rocker arm throw, with significantly less than twice the length and no increase in circumference, yet retaining the ability to control CR from a single point.

Balancing the Sanderson Mechanism can be done to near perfection. The motion of the pistons is almost perfectly sinusoidal for all values of CR; all even harmonics are missing, and the third harmonic is the largest at about one percent. There are no net forces with a symmetrical arrangement of three or more pistons. The only concern then is primary moment balance, and this turns out to be a matter of adjusting two counterweights to cancel the rotating couple moments generated by the piston motion. The smoothness of the mechanism is phenomenal, better than a precision balanced electric motor of similar size. Some advantages of such fine balancing are of course simpler engine mounts, less engine wear, less noise, and greater passenger comfort.

Easy scalability of the SED system is anticipated, from very small to several thousand horsepower, based on systems that have already been built, from a fractional horsepower to 500 horsepower.

We estimate that an automobile getting say, 30 mpg with a conventional engine, equipped with a CEI/SED engine of the same horsepower, could achieve a gas mileage in the neighborhood of 50 mpg. With the addition of the SED hydraulic hybrid feature, that gas mileage would reach over 60 mpg, with the lowest possible tailpipe emissions, and other features already mentioned, such as smooth operation. Equally important, when viewed from a cost and simplicity perspective, the CEI/SED engine provides advantages that are groundbreaking when the very low cost and simplicity of the system are factored in. Widespread adoption could mean oil independence of the United States, and the ability to provide such low tailpipe emissions so as to meet tough projected requirements for "the engine of the future" for the next two decades, and possibly longer, until a new form of energy is discovered, developed and commercialized.

February 12, 2004

Albert E. Sanderson, Ph.D.
Sanderson Engine Development, LLC
Upton, MA 01568 U.S.A.
(508) 478-4454

Michael A. V. Ward, Ph.D.
Combustion Electromagnetics, Inc.
Arlington, MA 02476 U.S.A.
(781) 641-0520