Bob Bourque - New Steam Engine

Chapter	Title
1	Background
2	Motivations For This Engine
3	Requirements and Constraints
4	Progress
5	Prototype Development
6	Description of the Bourque Cycle
7	Features of the Cycle
8	The Complexity Issue
9	Fuel Requirements
10	First Example Engine in a Vehicle
11	Description of the Expander
12	Expander Hot Cylinder Lubrication
13	Expander Piston Structural Analysis
14	Two More Engine and Vehicle Examples
15	Other Engine Components
16	Materials
17	Safety
18	Water Freezing
19	Control System
20	Starting Time
21	Summary
	Acknowledgments
	Some Unit Conversions
	Notes and References

A Compact Pollution-Free
External Combustion Engine
with High Part-Load Efficiency

3. Requirements and Constraints

In order to maximize net, i.e. useful, efficiency for any power cycle, the average steam heat addition temperature must be maximized and the average heat rejection temperature minimized. The key word here is average. Peak temperatures are useful only in as much as they increase the average.

Peak temperatures are limited by materials. These need the following properties:

Capable of carrying the required internal stress at maximum operating temperature with acceptable safety margins

Forgiving (i.e. ductile)

Affordable

Available in large quantities

Capable of being mass-produced and joined

To be sure, exotic materials can be considered, but their use should be minimized.

Minimum temperatures are limited by the medium to which heat is rejected. Here it is ambient air, taken for design purposes to be 24°C (75°F). There are also restrictions on the size, particularly frontal area, of the condenser. This requires heat rejection temperatures to be much higher than the ambient air.

It is also necessary to maximize expander isentropic and mechanical efficiencies, and minimize parasitic losses from pumps, air blowers, flow pressure drops, and heat conduction. As discussed below, these have been done here.

In order to be competitive, a steam engine for automotive use must achieve the following:

In-use efficiency must be significantly greater than a gasoline engine

It must be truly multifuel and capable of accepting any fuel mixture at any time

It must fit entirely in the engine compartment with access for maintenance

It must condense all the steam using ambient air

The condenser must fit into the usual radiator space

The combustion temperature must stay below the level where NOx forms

The fuel must be completely burned

There must be rapid response to power changes

It must be fairly quick starting

In summary, for an automotive application with all its constraints, it is necessary to “pull out all the stops” and do everything possible to achieve the above requirements.

The Bourque Steam Engine

A Compact Pollution-Free External Combustion Engine with High Part-Load Efficiency

A Compact Pollution-Free
External Combustion Engine
with High Part-Load Efficiency