Burner-heat exchanger assembly for an external combustion engine

1. Gas burner-heat exchanger assembly for an external combustion engine, comprising a gas burner and a heat exchanger,

the gas burner comprising:

a front wall defining a front side of the gas burner and forming a pass-through opening for the exchanger,

a rear wall defining a rear side of the gas burner and forming an opening to exhaust combustion gases,

a tubular side wall extended between the front wall and the rear wall and about a longitudinal axis of the assembly,

a tubular diffuser wall arranged inside the side wall and extended between the front wall and the rear wall and about the longitudinal axis, the diffuser wall having a perforation for the passage of a gas mixture from an outer side of the diffuser wall to an inner side of the diffuser wall where combustion takes place,

an annular distribution chamber formed between the side wall and the diffuser wall to distribute the gas mixture on the outer side of the diffuser wall,

a combustion chamber formed inside the diffuser wall and delimited on a rear side by the rear wall, the combustion chamber receiving the heat exchanger,

wherein the heat exchanger is formed by a tube assembly extended in the combustion chamber and passed through by a working fluid of the external combustion engine and having a heat exchange surface exposed in the combustion chamber,

wherein a minimal diffuser-exchanger distance between the diffuser wall and the corresponding heat exchange surface ranges from 20 mm to 40 mm.

2. The gas burner-heat exchanger assembly according to claim 1 , wherein the diffuser wall is substantially cylindrical and coaxial to the longitudinal axis and the heat exchanger forms a group of radially external heat exchange surfaces arranged along a circumference about the longitudinal axis, wherein the minimal diffuser-exchanger distance, measured in a radial direction with respect to the longitudinal axis, is:

C=D×A×K/(B×D−2×A×K)+tolerance,

where:

A is the longitudinal height of the perforated area of the diffuser wall,

B is the longitudinal height of the heat exchange surfaces inside the combustion chamber,

D is the external diameter of the heat exchanger inside the combustion chamber, K=23,6747,

wherein the tolerance is ±7 mm.

3. The gas burner heat exchanger assembly according to claim 1 , wherein a longitudinal height of the perforated area of the diffuser wall ranges from 80 mm to 100 mm, a longitudinal height of the heat exchange surfaces inside the combustion chamber ranges from 80 mm to 100 mm, and an external diameter of the heat exchanger inside the combustion chamber ranges from 175 mm to 190 mm.

4. The gas burner heat-exchanger assembly according to claim 3 , wherein the longitudinal height of the perforated area of the diffuser wall is A=90 mm, the longitudinal height of the heat exchange surfaces inside the combustion chamber is B=90 mm, and the external diameter of the heat exchanger inside the combustion chamber is D=183 mm.

5. The gas burner-heat exchanger assembly according to claim 4 , wherein the minimal diffuser-exchanger distance ranges from 29 mm to 35 mm, preferably 32 mm.

6. The gas burner-heat exchanger assembly according to claim 1 , wherein the heat exchanger comprises a plurality of straight tube lengths parallel with respect to the longitudinal axis.

7. The gas burner-heat exchanger assembly according to claim 1 , wherein the heat exchanger comprises U-shaped tubes, wherein the two legs of the “U” form straight lengths parallel with the longitudinal axis.

8. The gas burner-heat exchanger assembly according to claim 7 , wherein the U-shaped tubes are all oriented in planes radial with respect to the longitudinal axis and form a first tube assembly, radially more external, which alternates with tubes, radially more internal, of a second tube assembly, wherein all the tubes of each assembly have a same radial distance from the longitudinal axis.

9. The gas burner-heat exchanger assembly according to claim 1 , wherein the diffuser wall is internally coated with a mesh or fabric layer forming an internal combustion surface of the diffuser wall.

10. External combustion engine comprising a gas burner-heat exchanger assembly according to claim 1 .

11. The gas burner-heat exchanger assembly according to claim 1 , wherein the external combustion engine comprises a Stirling engine.

12. The gas burner-heat exchanger assembly according to claim 2 , wherein the tolerance is ±3 mm.

13. The gas burner-heat exchanger assembly according to claim 2 , wherein the tolerance is ±1 mm.

14. The gas burner-heat exchanger assembly according to claim 4 , wherein the minimal diffuser-exchanger distance is 32 mm.