Beyond the State of the Art
The following analysis provides an overview of the performance level of the Libralato Engine, compared with the dominant 4-stroke technology
Power-to-weight ratio
Reasoning: 100 % gain is possible since there is one combustion cycle per revolution instead of one every 2 revolutions in a 4 stroke. Since many components like the camshaft, connecting rods, valve controlling device are not present considerable weight is eliminated.
Gain over Conventional ICE: +100% kW/kg
Combustion Efficiency level
Reasoning: The expansion volume of the Libralato engine is larger than the compression volume, allowing complete expansion of the gases (similar to Atkinson Cycle). Thermodynamically this allows the maximum amount of chemical energy from the fuel to be converted into mechanical work.
Thermodynamically, the Libralato engine is estimated to produce a 5.5% increase in efficiency over conventional 4 stroke piston engines. In conventional 4 Stroke engines the combustion expansion of the gasses is equal to the compression therefore the amount of chemical energy from the fuel that can be converted into mechanical work is restricted.
Figure 6. Atkinson Cycle
Gain over Conventional ICE: +5.5%
High torque / Constant torque
Reasoning: The force created by the combustion is directly placed on the output shaft instead of a connecting rod – rod bearing – crankshaft setup, which result in energy losses. In piston engines the piston is at the end of the cylinder when the ignition occurs, therefore having a fully extended connecting rod does not permit the configuration to transfer torque immediately to the crankshaft.
As the pressure of the combustion gas decreases, the working surface area of the leading rotor increases and therefore a fairly constant torque is placed on the output shaft over 150 degrees. Since the effective combustion cycle is 170 degrees per revolution, two banks (engines) could be used in series to result in 340 degrees of constant torque output.
Gain over Conventional ICE: TBD (N-m)
Regulated Emissions
Reasoning: The first compression phase of the Libralato engine controls the later scavenge of the exhaust gases. This scavenge phase has several functions. Firstly, it helps to oxidise the exhaust gases more fully. Secondly, it reduces the temperature of the exhaust gases. Thirdly, the scavenge air can be re-circulated within the engine to act again in the compression phase. Finally, it avoids an extra phase for the mechanical expiration of the exhaust gases.
Although the Libralato engine offers major advantages used with any fuel, potentially the greatest advantages of the design are realised when used with diesel or biodiesel fuel blends. Traditionally exhaust gas recirculation (EGR) has been used as a means of reducing peak temperature during combustion. Since the exhaust gas does not participate in the combustion process it absorbs some of the energy and hence lowers the peak temperature and reduces NOx formation. The scavenge phase provides a high-velocity air stream and turbulent mixing of the combustion by-products. The increased oxygen concentration further enhances particulate matter (PM) oxidation and helps burn up the PM as they form. Because NOx is formed early in the combustion cycle, adding air later in the cycle does not increase NOx. With the amount of excess air almost doubled, both NOx and PM should be reduced simultaneously by about 50%. Since Diesel engines operate at an overall lean fuel-air ratio, they already tend to emit low levels of hydrocarbons (HC) and carbon monoxide (CO). Excess air will however show a further reduction in HC and CO emissions. Because the Libralato engine is based on high excess air capacity it is not sensitive to fuel sulphur content.
Gain over Conventional ICE: -50% NOx & PM
Noise level
Reasoning: The noise level is caused from the gasses exiting the combustion chamber at high pressure. In the Libralato engine the gasses exit through a very large orifice and exit at only 3 atmospheres due to the full combustion that takes place. In 4 stroke engines the noise level is dampened by a catalytic converter, which also functions to reduce the levels of emissions. Therefore in applications such as cars the Libralato engine would not require the ancillary systems of catalytic converter plus noise damper. In smaller portable applications (leaf blowers) where catalytic converters are non existent, the inherently reduced noise level produced by the Libralato engine would be more obvious.
Gain over Conventional ICE: -50% dB
Vibration level
Reasoning: About 30% reduced (requires further simulation). The engine has a total of 4 moving parts, and there is a uniform distribution of weight in the engine as it rotates (test done using 4 weight scales). The 4 moving parts never undergo drastic changes in acceleration, as is the case with the cylinder head when it reaches the two extremes of the stroke.
Gain over Conventional ICE: -50% m/s2
Number of components
Reasoning: Number of components in a Libralato engine: (Engine block, Leading
rotor, Following rotor, Rotor bearings, Connecting rod, Face rings, Head
gasket, Drive shaft, Main bearing, Intake manifold, Throttle, Fuel injector,
Cooling fins, Water jacket, Rotating exhaust, Exhaust system, Exhaust
manifold, Fan, Fuel pump, Oil pump, Radiator, Spark plug, digital engine
management unit, starter: 24
Number of components in a 4 Stroke engine: (Block, Cylinders, Entry & Exit
valves, Camshaft, Piston, Piston rings, Connecting rod, Connecting rod
bearing, Crankshaft, Flywheel, Main bearing, Crankcase, Head, Head Gasket,
Intake manifold, Throttle, Choke, Carburetor / Fuel injector, Cooling fins,
Water jacket, Exhaust system, Exhaust manifold, Catalytic converter, Fan, fuel
pump, Oil pump, Oil sump, Radiator, Spark plug, engine control unit, starter,
31
Gain over Conventional ICE: No of comp. -23%
Production cost
Reasoning: After proof of concept prototypes, pre-commercial prototypes will be evaluated to fully analyse the cost of manufacturing the engine in high production volumes. The Libralato engine will inherently cost less than a 4 stroke engine due to low number of components (25 vs 35) and the reduced tolerances required for critical components.
Gain over Conventional ICE: TBD
Maintenance costs
Reasoning: A figure for this can be given once extensive bench testing is performed on the engine, however based on only 4 moving parts and the avoidance of sealing problems such as in Wankel engines, the maintenance costs for the Libralato engine should be significantly reduced.
Gain over Conventional ICE: TBD
Reliability
Reasoning: A figure for this can be given once extensive bench testing is performed on the engine, however based on only 4 moving parts and the avoidance of sealing problems such as in Wankel engines, the maintenance costs for the Libralato engine should be significantly reduced.
Gain over Conventional ICE: TBD
Cooling
Reasoning: A figure for this can be given once extensive bench testing is performed on the engine. There is relatively uniform thermal dispersion across the entire engine due to the constant recirculation of air, and the mechanical interaction between the two sides. This uniform thermal dispersion implies the need for less cooling of the hotter side of the engine (which is an issue in the Wankel engine). Since engine cooling is a process that taps into the combustion energy source, uniform temperature dispersion would reduce this loss.
Due to constant recirculation of air inside the engine there is less time required for engine heat up during the start up and therefore less time is needed until optimum efficiency temperatures are reached by the engine.
Gain over Conventional ICE: TBD
