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Create The Future Design Contest

Modified Stirling Engine With Greater Power Density Category: Transportation

James Hacsi
independent inventor
Pueblo, CO US
Page Views: 1,413
Votes: 8
Entered: 07/14/2008

Stirling engines are some of the most efficient engines known, but they unfortunately have little output power for their size and weight. In other words, they have low power density and low specific power. Concepts taken from a patented internal combustion engine with a sidewall combustion chamber(US patent 7,387,093) were used to improve the output power of a Stirling engine. A displacer piston is added to act in opposition to the power piston in the power cylinder, and both pistons cover or uncover ports (with their side skirts) leading to the cold-cylinder and heater. The entire purpose of this modification is to give additional time for the gas or air to heat while it is trapped inside the heater (180 degrees of the cycle!) in order to increase the hot-side temperature and the Carnot efficiency. Additionally, the entry of extra-hot gas or air into the power cylinder is delayed until the power piston is 90 degrees into its power stroke so that maximum torque is developed to rotate the crankshaft. Before that point, the connecting-rod is mostly vertically-aligned with the cylinder-wall and most of the available energy is wasted trying to drive the crankshaft through the bottom of the engine! Delaying gas-entry into the power cylinder until the power piston is at 90 degrees past top-dead-center increases the output power of the engine by 6 to 7 times, while simultaneously improving the theoretical Carnot conversion efficiency! Use of a displacer piston in the power cylinder acts to decrease cylinder-volume so gas-entry into the power-cylinder has maximum effect while also allowing the cold-cylinder piston to extract even more work from the expanding gas (air). As you may know, the power piston and cold-cylinder piston move 90 degrees out-of-phase, and the displacer piston is driven by a separate drive mechanism. The power piston, driven by momentum of the crankshaft, initially compresses air into the heater and cold-cylinder through both open ports, but it blocks the bottom port when at 90 degrees into the compression stroke which allows the air to begin to heat in the heater. Air still flows between cylinders through the top port until the piston reaches top-dead-center. At that point, the displacer piston follows the power piston down the cylinder covering the top port which means the gas is entirely trapped in the heater while the cold-cylinder piston attempts to compress air into the power cylinder (but it can't). At 90 degrees into its power stroke, the power piston uncovers the bottom port and the displacer piston is rigidly locked into position so that a tremendous release of energy occurs... Pow! Maximum force is applied to the power piston at precisely the right time when most of the applied force effectively rotates the crankshaft. This engine has the power of a steam engine (without the steam!) and can be used in a hybrid-electric vehicle with greater power and conversion efficiency. The modifications also allow a more rapid response to acceleration changes than a normal Stirling engine.


Meet the Entrant, James Hacsi

  Contact Email:
  Association: independent inventor
  Profession: government
  Number of times entering contest previously: 1
  Design Tools:
Pencil and Paper
Physical models
Image rendering software
Analysis software
  Software used:
  James's favorite design tool:
CAD software because of the amazing flexibility, adaptability, and ease-of-use

  James's hobbies and activities:
most outdoor sports, but I love surfing the internet to find all the new evolving technologies, especially when they are energy-related
  What role does James believe product design plays in creating a better future?
A vital role because new devices can be developed rapidly so the products can be introduced commercially very quickly

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