Advantages of Libralato Engine
POWER-TO-WEIGHT RATIO The Libralato engine is predicted to deliver a 100 % gain in power to weight ratio compared to a 4-stroke reciprocating engine, since there is a combustion phase in every revolution instead of one in every two revolutions in a four stroke engine. The design radically reduces the number and complexity of components required e.g. valvetrains, pistons, con-rods, crankshafts, cam shafts etc. Therefore considerable weight is eliminated.
COMBUSTION EFFICIENCY LEVEL - 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 4% increase in efficiency over conventional 4 stroke piston engines. In conventional 4 Stroke engines the combustion expansion of the gases is equal to the compression therefore the amount of chemical energy from the fuel that can be converted into mechanical work is restricted. The Libralato engine possesses a novel combustion chamber, free from valves, which can be independently sized and shaped to provide optimum gas dynamics and combustion.
HIGH TORQUE / CONSTANT TORQUE - 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. In the Libralato engine, 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 (equivalent to pistons) could be used in series to result in 340 degrees of constant torque output.
Regulated Emissions The Libralato engine is predicted to meet Euro 6 emission standards for four principle reasons.
- Due to the asymmetrical geometry, combustion of the fuel in the expansion chamber is more efficient and more complete, reducing HC, CO and PM emissions
- Elimination of the localised high temperature zones seen in the fuel-rich regions of 4-stroke engines should greatly reduce NOx formation in the Libralato engine
- The residual exhaust gases in the expansion chamber are completely scavenged by the fresh air from the first stage compression
- Since the engine can produce the same power as an in-line four cylinder engine with only two rotor banks, the demands on the after-treatment system should be considerably reduced
NOISE LEVEL - The noise level from conventional engines is largely caused by the mechanical reciprocation of parts (e.g. poppet valves, piston heads etc) plus the exhaust gases exiting the combustion chamber at high velocity. The noise level of the Libralato engine is predicted to be 50% lower due to the elimination of these reciprocating parts and the lower pressure and lower velocity of the exhaust gases exiting through the large and fast opening exhaust port. Therefore the Libralato engine is predicted to be exceptionally quiet, a characteristic highly desirable for plug in hybrid vehicle applications.
VIBRATION LEVEL Rotary engines are well known for having very low vibration and the Libralato engine is predicted to reduce vibration by about 70% (requires further simulation). The engine has a total of 4 moving parts and there is a uniform distribution of weight as the engine rotates. The 4 moving parts do not undergo drastic changes in acceleration, as is the case with reciprocating engines when the piston head reaches the two extremes of the stroke. Tests done using 4 weight scales and from analysis of the Pro-Engineer model of the Libralato engine show rotor bearing epicenter variation of less than 3mm.
COOLING - There is relatively uniform thermal dispersion across the entire engine due to the circulation of fresh air via the intake and scavenge phases. This thermal dispersion lowers the need for cooling the hotter side of the engine (which is an issue in the Wankel engine). FEA and CFD modeling plus close attention to the design of the lubrication and cooling systems of the engine are expected to fully address this aspect.
LUBRICATION - A design for a fuel pump integral to the internal mechanism of the engine has been patented (Italy only). Lubrication is an obvious area of concern, but this challenge will be fully addressed during the project.
SEALING - This is another obvious area of concern. However, unlike the Wankel engine, the Libralato engine has large sealing surface areas (equivalent in size to pistons) and each rotor is fixed by its own bearing and does not rely on its fit with the rotor housing for its location. The project will fully address the engine sealing, examining various configurations of scrapper seals, lateral sealing and sealing between components.
PRODUCTION COST - The Libralato engine is expected to cost in the region of 30% less than a 4 stroke engine of equivalent power output due to the elimination of major components (e.g. valvetrains, pistons, con-rods, crankshafts, cam shafts etc), reducing the number of moving parts (typically 37) to four and reducing engine mass by about 50%. Because the efficiency gains of the engine are due to its fundamentally new design and its revolutionary new thermodynamic cycle, it is anticipated that reliable engines can be produced with relatively low tech production engineering i.e. naturally aspirated, low pressure injection, low BMEP, low manufacturing tolerances.
RELIABILITY & MAINTENANCE COSTS - A figure for this can be given once extensive bench testing is performed on the engine. However, based on only four moving parts and the avoidance of heating, sealing and bearing wear problems such as in Wankel engines, the maintenance costs for the Libralato engine should be significantly reduced.