Steam output control system

A control system for a dual-fluid cycle engine, which includes a waste heat boiler for recovering waste heat from the engine exhaust gases, comprising control means for following a control path defined by the locus of peak efficiency points at reduced loads, where the control path results in a declining turbine inlet temperature as the load decreases, and wherein said control means comprises:

• (a) a first control system for controlling the Brayton cycle part of the dual-fluid cycle engine;
• (b) a second control system for controlling the Rankine part of the dual-fluid cycle engine;
• (c) memory means for setting the desired operating points of said first and second control systems, where the memory means contains predetermined settings for each of the two control system for all load conditions;
• and
• (d) means for regulating the Rankine cycle working fluid comprising a valve between the superheater and evaporator sections of the waste heat boiler.

In a dual-fluid heat engine comprising:

• a chamber;
• compressor means for introducing a first gaseous working fluid into said chamber, said compressor means having a predetermined pressure ratio (CPR);
• means for introducing a second liquid-vapor working fluid in the form of a vapor within said chamber at a defined second/first working fluid ratio (XMIX);
• means for heating said first gaseous working fluid and said second working fluid in the vapor form in said chamber at a defined specific heat input rate (SHIR);
• turbine means responsive to the mixture of said first and second working fluids for converting the energy associated with the mixture to mechanical energy, the temperature of said mixture entering said turbine means defining the turbine inlet temperature (TIT);
• counterflow heat exchanger means including at least superheater and evaporator sections for transfering residual thermal energy from said exhausted mixture of first and second working fluids to said incoming second working fluid to thereby preheat the same to a superheated vapor state prior to its introduction within said chamber, and wherein XMIX and SHIR are selected so that for a given value of TIT, XMIX is substantially equal to or is greater than XMIX.sub.peak, where XMIX.sub.peak occurs when the following conditions are both met simultaneously:
• (i) the temperature of the superheated second working fluid vapor is substantially maximized;
• (ii) the effective temperature of said exhausted mixture of the first and second working fluids is substantially minimized;
• and
• wherein the improvement comprises control means for controlling XMIX and SHIR along a maximum efficiency path as engine load varies such that as engine loads decrease, TIT is reduced, said control means including a valve located between the superheater and evaporator sections of said counterflow heat exchange means.

The method of operating a dual-fluid heat engine at partial load conditions, which engine comprises:

• a chamber;
• compressor means for introducing a first gaseous working fluid into said chamber, said compressor means having a predetermined pressure ratio (CPR);
• means for introducing a second liquid-vapor working fluid comprising water in the form of superheated steam within said chamber at a defined second/first working fluid ratio (XMIX);
• means for heating said first gaseous working fluid and said second working fluid in the vapor form in said chamber at a defined specific heat input rate (SHIR);
• turbine means responsive to the mixture of said first and second working fluids for converting the energy associated with the mixture to mechanical energy, the temperature of said mixture entering said turbine means defining the turbine inlet temperature (TIT);
• counterflow heat exchanger including at least superheater and evaporator sections means for transfering residual thermal energy from said exhausted mixture of first and second working fluids to said incoming second working fluid,
• said method comprising the steps of:
• preheating the second working fluid in the heat exchanger to a superheated vapor state prior to its introduction within the chamber;
• and
• selecting XMIX and SHIR so that:
• (a) for a given value of TIT, XMIX is substantially equal to or is greater than XMIX.sub.peak, where XMIX.sub.peak occurs by both
• (i) maximizing the temperature of the superheated second working fluid vapor;
• and
• (ii) minimizing the effective temperature of the exhausted mixture of the first and second working fluids;
• and
• (b) TIT decreases as engine load decreases;
• and
• regulating a control valve located between the evaporator and superheater sections of the waste heat boiler for regulating XMIX.