A different approach to heat-driven power.

In the ideal adiabatic reference model, the piston compresses the gas on its inward stroke, raising its temperature adiabatically. On the outward stroke, the gas expands against the piston, performs work, and cools adiabatically.

These processes preheat the working gas before external heating and precool it before external cooling. The design uses those temperature changes to reduce the additional heating and cooling required during the cycle.

The isolator directs the working gas’s thermal exposure: shielding the cold cap during heating and shielding the hot cap during cooling. Closely mating surfaces minimize the gas remaining outside the intended heating and cooling process.

Current analysis also investigates adding heat during expansion and rejecting heat during compression. The objective is to move those portions of the cycle toward approximately isothermal (constant-temperature) behavior, alongside adiabatic portions and approximately constant-volume heating and cooling transitions.

The closely mating caps and moving isolator are intended to coordinate thermal exposure with piston motion. How closely the working gas can follow the intended temperature path depends on heat-transfer rate, timing, flow resistance, and operating speed.

This mixed-cycle approach is under investigation. Ideal-cycle calculations provide reference cases; they do not establish the efficiency or output of a working engine.

Robert Stirling’s 1816 invention introduced a regenerative approach to recovering heat. A conventional regenerator absorbs heat from gas moving toward the cold region and returns that heat as gas moves toward the hot region.

The MDE architecture instead uses compression and expansion to obtain its intended intermediate temperatures, with the thermal exposure controlled by the isolator. It operates without a conventional regenerator and its associated heat-storage matrix and flow path.

The MDE patent describes a design objective of less than one percent dead volume, defining dead volume as working gas that is not alternately heated and cooled. This minimizes a major design penalty encountered in conventional hot-air engines.

The power-piston cylinder connects near the chamber’s central region. The arrangement provides gas communication with the piston cylinder without requiring the gas to pass first through the opposite thermal end.

Most four-stroke gasoline and diesel internal combustion engines (ICEs) have one power stroke per cylinder every four piston strokes.

A single-acting MDE chamber is intended to provide one expansion event every two strokes. A double-acting external combustion engine (ECE) uses both faces of its power piston, providing an expansion event in each direction of travel. James Watt included the double-acting steam-engine principle in his 1782 patent.

One four-stroke internal combustion cylinder operating at 3,000 revolutions per minute (rpm) makes 6,000 strokes per minute, including 1,500 power strokes. A double-acting MDE piston at 750 rpm makes 1,500 strokes per minute, with an intended expansion event on every stroke.

This event frequency creates an opportunity to obtain useful power at substantially lower rotational speed. Actual output also depends on the work performed during each event, including compression work and the pressures acting on both piston faces.

With comparable effective working areas and work per face, double acting can approximately double ideal indicated output relative to a single-acting arrangement. It also requires corresponding heating and cooling capacity; rod areas and real losses must be included.

Lower speed gives heat more time to enter and leave the working gas during each cycle and may reduce some sources of mechanical wear. Substantial power at low speed produces high average torque.

Multiple double-acting modules can be combined for greater output. Appropriate phasing can also produce smoother torque delivery.

The Maximum Delivery Engine architecture may be used with known or later-developed technologies without changing the underlying MDE architecture. Examples include double-acting piston arrangements, corrugated or enlarged heat-transfer surfaces, extended hot- or cold-cap geometries, integrated generators or flywheels, battery-assisted hybrid systems, and drivetrains for vehicle propulsion.

Our preliminary calculations begin with the ideal MDE cycle and use an approximate 20% allowance for remaining practical losses. The allowance excludes conventional-regenerator losses because the MDE has no conventional regenerator, and it does not assign the large inactive-volume penalty associated with conventional Stirling arrangements.

Residual clearances, heat-transfer limitations, thermal leakage, gas-flow resistance, friction, sealing, and auxiliary loads still require evaluation. The allowance is an engineering estimate to be refined through testing.

Ideal indicated power describes calculated work within the engine. Shaft power is the useful mechanical output after mechanical losses. Electrical output additionally depends on the generator and operating auxiliaries.

Fuel efficiency also includes the effectiveness of combustion and heat delivery to the working gas.

Historical external-combustion research provides evidence for the potential to substantially reduce noise and combustion-related pollutants compared with internal combustion engines.

The MDE separates combustion from the sealed working gas. This allows the burner to be designed around controlled fuel delivery, air supply, mixing, and combustion quality, independently of the moving power piston.

Research on other external-combustion engines has demonstrated very low pollutant emissions without catalytic converters. These results provide a strong basis for pursuing cleaner MDE power.

Startup is an important part of that development. An external burner avoids burning fuel inside a cold, lubricated power cylinder and provides a different route to controlling ignition and warm-up emissions. Reducing those emissions is a specific development objective.

Historical research: Environmental Protection Agency review, noise section 5.3.4; General Motors noise and emissions research; Multifuel Stirling vehicle emissions testing. These findings concern the tested historical engines.

The MDE patent establishes the architecture. Current performance figures are calculations and engineering estimates; prototype testing will establish actual power, efficiency, noise, emissions, and durability.

The updated technical brief explains the MDE architecture, its mixed thermodynamic approach, preheating and precooling without a regenerator, dead-volume objectives, and double-acting configurations. It includes an ideal-cycle efficiency reference and supporting literature.