CEM Engine

[Allen]

Okay.... I'll post the article.. >/ Why can't you people just click links.


It's an interesting design.


The concept of the CEM engine begins with the essential components of internal combustion: a combustion chamber (or cylinder) and an air compressing device (or piston). At the heart of the CEM is a shaft-mounted cylinder block featuring six piston chambers or bores. The cylinder block is a two-piece design machined with six bores and a driveshaft passage. A 6-piston configuration was arrived upon based on two theoretical advantages over a 4-piston design, which will be discussed further in the text. While current technology can offer a small single- or dual-cylinder engine, the relative power-to-weight and -displacement ratios of a 1- or 2-cylinder engine of conventional design indicate that their level of power output would not be sufficient to meet a minimum 4 brake horsepower (bhp) requirement.



Power output characteristics for any given bore and stroke combination can be derived through a standard theoretical performance calculation based on a conservative brake mean effective pressure (BMEP). In this case, a BMEP of 180 (equivalent to a standard high-output automobile engine) was used as a baseline. The CEM’s bore diameter of 0.75 inch with a stroke of 0.75 inch was determined by computational analysis of the overall weight and scale requirements for the engine. Having a stroke length equivalent to bore diameter (a bore/stroke ratio of 1:1) is the optimum combination for the CEM engine as it creates a maximum torque angle of 26.7 degrees with minimum drive pin stress at the mid point of the cam sleeve ramp. A bore radius of 0.375 inches will place the surface area of the piston at approximately 0.44 square inches. The design of the CEM piston is the true innovation of this new technology. The CEM piston is double-ended: Each half is a mirror image of the other, which allows the 6-piston CEM to function as a 12-cylinder engine. A second-generation CEM piston design utilizing the same concept but incorporating a modular assembly that would increase power through a reduction in moving mass, and minimize machining and material costs.



The original CEM piston (below, left) now used primarily in pump applications is a solid design machined from aircraft-grade aluminum alloy. Hardened steel drive pins are hydraulically pressed into position.



The second-generation CEM piston (above, right) designated for use in the CEM engine is a modular concept. Manufacturing considerations influenced this redesign, however it is not without dynamic benefit. Friction and stress analyses will determine the composition of metals that will be used for the engine.



Regardless of the CEM piston's direction of travel within the cylinder, there is no downward stroke as with a standard crank-driven piston. One of the main limiting factors of engine revolutions per minute (rpm) in a conventional pushrod engine is the connecting rod-to-piston angle during the transition phase from down stroke to upstroke, and also piston-to-valve clearance at top dead center. The continuous motion of the CEM piston's stroke increases the rpm ceiling substantially by eliminating the possibility of either condition.

Calculating the displacement of an engine is important for establishing an elementary basis for comparison of specific power outputs (i.e. horsepower per cubic-inch displacement ratios). The CEM engine's total swept volume of piston displacement in cubic inches (cid) is 3.9760 based on a 0.75" bore and 0.75" stroke calculated as follows:

Total Displacement = pi/4 x bore diameter squared x stroke x # of cylinders

0.7853982 x 0.5625 x 0.75 x 3.9760cid

As indicated in the specifications chart, the calculated horsepower of 6.51 gives the CEM a horsepower-to-displacement ratio of 1.6:1, which would place it in the high-output performance category. The apparent efficiency of the CEM engine is a product of its unique combustion process.


BORE RADIUS 0.375 "
BORE DIAMETER 0.75"
STROKE 0.75"
PISTON SURFACE AREA 0.44 SQUARE INCHES
NUMBER OF CYLINDERS 12
4-STROKE CYCLES PER REVOLUTION 2
NUMBER OF POWER STROKES PER MINUTE 43200
PULSES PER SECOND 1440 PPS
PULSES PER MINUTE 86400 PPM
RPM OF ENGINE 3600 RPM
VOLUME IN CUBIC INCHES AT SPEED 51529973.5 CUBIC INCHES
VOLUME IN CUBIC FEET AT SPEED 29820.59 CUBIC FEET
DIAMETER OF ENGINE 3.75 INCHES
LENGTH OF ENGINE 4.5 INCHES
DISPLACEMENT OF TOTAL ENGINE BODY 49.7 CUBIC INCHES
DISPLACEMENT OF TOTAL ENGINE BODY 0.03 CUBIC FEET
TOTAL DRY WEIGHT 3.718 POUNDS
MEAN EFFECTIVE PRESSURE 180 PSI
FOOT POUNDS PER MINUTE PER HP 33000
TORQUE 9.49 LBS-FEET
INDICATED HORSEPOWER 6.51 HP
MEAN PISTON SPEED 900 FEET/MINUTE

Figure 1.1-5 This curve of the CEM covers one full shaft rotation. In theory, with all 12 cylinders firing, the resulting torque overlap will provide a desirable flat curve over a broad rpm spectrum.

[Allen]

Each CEM piston is outfitted with a centrally fixed drive pin, which extend ******d through an axial slot machined into the cylinder block. Each drive pin serves to guide the movement of the piston within its bore as the cylinder block rotates. Because there is no crankcase, per se, for combustion blow-by to escape into, there is no need for venting the CEM cylinder assembly as is required with a conventional piston engine. A high-compression version of the CEM will feature a step-gap-style piston ring constructed of a ceramic/graphite composite primarily for its friction-reducing properties rather than piston-to-wall sealing. A
low-compression CEM engine will not require piston rings, totally eliminating piston-to-wall friction in this version.


The conventional IC engine design must meet a fine balance between effective piston-to-wall sealing and engine failure due to piston-to-wall friction. This balance is a unique science of metallurgy and expansion/compatibility coefficients of known materials. A minute amount of compression loss into the crankcase is acceptable providing the allowed Delta Pressure is not disproportionate as with a set of worn rings creating excessive leakage. This blow-by constitutes a normal loss of compression and volume, which must be vented from the crankcase into the atmosphere. As running time accumulates, however, and ring/cylinder wall deterioration creates an abnormal volume of pressure loss into the crankcase, a major overhaul or engine failure becomes eminent.

The CEM assembly is radically different in this concept since venting of the cylinder block is not required, hence, total combustion efficiency is achieved. This occurs through compression chamber pressure equalization. The CEM engine’s compression/power stroke builds pressure within the cylinder block until it becomes equal to the combustion chamber pressure. A gas pressure seal is formed thereby sealing the combustion chamber as high-pressure flows to a low-pressure area.

The cylinder and pistons are the only moving parts in the CEM engine; a 6-piston/12-cylinder CEM therefore has 7 internal moving parts. When you consider the myriad rods, bearings, pins, shafts, and valves at motion within a conventional four-stroke engine or even a rotary-piston engine, it is not difficult to understand where the CEM gains its performance and durability advantages. Two 360-degree sleeve halves enclose the CEM piston/cylinder assembly. The inner edges of the two sleeves meet to form a concentrically located sinusoidal guide path or camtrack.. This camtrack serves as a guide for the CEM piston’s fixed drive pins to follow. As the cylinder spins, the piston reflects the path of the camtrack, so the degree and frequency of stroke becomes a precise element of the CEM’s sinusoidal design or “grind” (See Cam Assembly illustration above).

The CEM’s length of stroke is determined by the degree of zenith on either side of the camtrack’s center. As the drive pin guides the piston from one zenith to the other, the cylinder block rotates each cylinder into port alignment. The CEM cycle minimizes the intake-compression-power-exhaust pulsations, which are separated along the sinusoidal path to provide a very smooth transition of air/fuel mixture to power.


Normally, the function of introducing an air/fuel mixture would occur through intake manifolding to a cylinder head with a series of cam/pushrod-activated intake and exhaust valves controlling the flow of air and fuel until burned gases exit through an exhaust manifold. An efficient 6-cylinder engine typically uses a 24-valve (4 valves per cylinder) arrangement requiring dual camshafts and critical valve lash adjustments. The CEM relegates this entire process to passive intake and exhaust ports located in the cylinder heads that cap each end of the cylinder/piston/sleeve assembly.


The CEM uses two end plates, or cylinder heads, that combine the functions of intake and exhaust porting, intake manifolding, and combustion chambering (i.e. location of glow plug). Each CEM head contains one intake port and one exhaust port. The diameter of each of these ports precisely matches the diameter of the six identical bores in the cylinder. As the cylinder block rotates, each bore intermittently aligns with an intake or exhaust port depending on the cycle. The spacing between each bore is precisely equivalent to the bore diameter, meaning that each stroke of the cycle occurs without overlap. Also, because the cylinder head ports effectively match the diameter of the bores, volumetric efficiency is maximized with a virtually unrestricted air/fuel-exhaust flow.


Although the CEM engine can be built in a 4-piston/8-cylinder arrangement, the
6-piston/12-cylinder version yields two specific advantages. The first advantage results from a firing overlap produced from the out-of-phase alignment of pistons with their cam peak intervals. This out-of-phase overlap in timing of piston bore-to-port alignment delivers a smoother, more efficient firing cycle without relying on inertial energy. The second advantage is realized with the arrangement of the pistons. A 4-piston/8-cylinder CEM engine would have piston bores placed at 90-degree intervals. With each bore of a 6-piston/12-cylinder version located at a 60-degree interval and utilizing the same bore and stroke, a more favorable power-to-weight ratio is achieved simply from an increase in volume with the same engine casing and head dimensions that could be used in a 4-cylinder design.


The method for delivering fuel to the CEM can vary depending upon the intended use of the engine and the specific conditions under which it must operate. The extreme g-force condition of a gun launch or airdrop will undoubtedly pose limitations; however, it would be premature to rule out any options prior to further research. Testing of aspiration devices will focus on maintaining gun-launch and airdrop capability within a feasible cost-per-unit range beginning with a numerical analysis of the stress load factors of carburetor and injector components.

Normally, fuel for a diesel-burning engine is injected at pressures ranging from 10,150 psi (700 bar) to 21,750 psi (1500 bar). An injector pump capable of delivering fuel within this high pressure range will absorb approximately one eighth of the engine’s power and can weigh close to the total weight of the engine. Existing pumps come in a variety of designs that can be made adaptable to the CEM engine.

At this early stage of development, the prototype CEM engine design favors a tuned mechanical direct-port fuel injector at each intake port of the two cylinder heads. The design of the injector unit can be an easily replaceable/disposable pre-calibrated bolt-on unit or a specifically tuned integrated system built into the cylinder head at the intake port. The benefits of a bolt-on injector would offer on-location ease of service and lower per unit cost, while a more streamlined integrated injection system would provide a measurable horsepower advantage by optimizing the location of injector nozzle within the intake port/combustion chamber area of the engine. Manifolding a single injector to the two intake ports would be the most economical design but would compromise the engine’s compactness. Either style can be fed from a remote source via fuel line or from a onboard fuel cell.

The CEM engine offers a unique advantage in fuel delivery by its point of injector nozzle location relative to the combustion chamber. The CEM introduces fuel between the cylinders, allowing the pre-pressured cylinder on compression/power cycle to rotate to the injector port. This action results in a rapid increase in both cylinder pressure and air/fuel charge temperature to promote combustion. As a result of the CEM’s port-to-cylinder relationship, precision mechanical port timing of ignition is not only possible but variable as well.

Injector nozzle design relating to degree and pattern of atomization as well as volume of air/fuel mixture will be determined during modeling and analysis of theoretical performance curves. One design in particular that we are investigating is the Babington Unaspray system for its ability to deliver atomized fuel at a notably lower pressure by means of a premixing chamber. Such a system can be integrated into a lightweight injection system capable of fuel atomization in the 50- to 150-micron range. A Photostat treatment will reduce these medium-sized fuel particles to the 7- to 20-micron size. As per requirement, the CEM is being developed to burn diesel, which is categorized as a shipboard-safe “heavy” fuel.

[Allen]

A tuned exhaust system is an integral part of a balanced high-performing engine. It must efficiently perform two distinct functions: expel hot gasses and deaden or dissipate sound energy. Unfortunately, one is done at the expense of the other. Another non-exhaust-related function of this system is to pressurize the fuel tank, which may or may not apply in certain applications. Where space and size are not factors, a system can be designed to handle both tasks of gas removal and sound dissipation with little or no compromises. A viable option for the CEM is a compact chambered exhaust tube bolted directly to the exhaust port. Space permitting, the exhaust tube should incorporate an expansion chamber to aid in heat dissipation and control of backpressure. Variations in tube diameter and baffling elements will also effectively regulate airflow velocity and backpressure, but the trade-off with any compact bolt-on system designed for maximum performance is going to be a limited capability of resonance control.

One other exhaust option for the CEM will be an exhaust diverter, which will consist of a tube or hose that connects the engine’s exhaust port to a remote muffling system. A diverter system of relatively short length will be simple to install on location and a proper design will have little or no negative effects on performance. An extensive diverter tube or hose, however, will tend to create an abnormal amount of backpressure and heat retention. If such a system is utilized, a dynamic flow test will be performed during Phase 1 to analyze and prevent this condition.

In parallel with the preliminary design process of the CEM engine, considerable research will be dedicated to the selection of materials utilized in the construction of the prototype components. Particular emphasis will be placed on the appropriate selection and counterpart of materials for the CEM piston drive-pins and cam sleeves, as this area constitutes one of the constant surface-to-surface contact points in the CEM where stress resistance and friction reduction are critical for extended periods of operation. Based on E.P. Industries’ prior development experience with similarly engineered CEM pumps and compressors, the selection for engine casing material is a 6000-series aluminum alloy, which has been determined to minimize weight as well as cost per unit. An anodic oxidized (anodized) aluminum alloy casing will provide maximum corrosion and chemical resistance with excellent thermal conductivity to maintain a low level of temperature variation.

CEM pumps have exhibited an excellent service life with dry friction sliding-contact internal components. This prolonged operation without a lubrication film on load-bearing surfaces is attributed to the qualities of ultra-high molecular weight polyethylene (UHMW-PE) along with self-lubricating lead-based brass and bronze alloys, which will receive the primary focus of evaluation for the prototype engine cam sleeves and pistons. Although possessing favorable coefficients of friction, economical price and no danger of seizing with metals, thermoplastics have a relatively low operating temperature and are subject to thermal expansion. To address this potential shortcoming, thermal and dynamic load analyses of materials for the CEM Engine will involve research and testing on metal-ceramic, carbon-graphite, polymer-metal and silica-based composites as alternatives.

Don't tell me about double posting, it was too long for just one.