Three low NOx combustors, i.e. a lean premixing combustor, a rich-lean two stage combustor and a lean diffusion flame combustor, were tested in order to find out a suitable combustion concept for an automotive ceramic gas turbine combustor. The prevaporization-premixing lean combustion was proposed as the most promising candidate to meet Japanese 10 mode regulation for gasoline passenger car. The required conditions for the uniform premixture formation in the prevaporization-premixing tube were achieved by a fine droplet size atomizer and by means of swirl and turbulent generator. Air ratio range, air loading and other dimension criteria in the lean primary combustion zone were also proposed in the present paper.

The performance of a regenerated gas turbine generator in the 3–5 kW power range has been analyzed to understand why its measured efficiency was on the order of 6% rather than the 20% suggested by consideration of its components’ efficiencies as measured on rigs. This research suggests that this discrepancy can be primarily attributed to heat and fluid leaks not normally considered in the analysis of large gas turbine engines because they are not as important at large scale. In particular, fluid leaks among the components and heat leakage from the hot section into the compressor flow path contributed the largest debits to the engine performance. Such factors can become more important as the engine size is reduced. Other non-ideal effects reducing engine performance include temperature flow distortion at the entrance to both the compressor and turbine. A cycle calculation including all of the above effects matched measured engine data. It suggests that relatively simple changes such as thermal isolation and leak sealing can increase both power output and efficiency of this engine, over 225% in the latter case. The validity of this analysis was demonstrated on an engine in which partial thermal isolation and improved sealing resulted in a more than 40% increase in engine output power.

Two aspects of reliability assurance are discussed. First, This paper deals with the reliability design of the emissions under transient conditions. The optimization was made from the simulation results of the relationship between the response of the variable combustor geometry to follow load changes and the resulting exhaust emission levels. The load variation pattern used in this investigation was that of the Japanese 10-mode regulation. Second, this paper describes the validity of the reliability design prepared for the ceramic liner of the combustor. A service life prediction was made for the liner on the basis of stress analysis results and fatigue parameters.

A low emission combustor for a 100kW ceramic gas turbine, which is intended to meet Japanese emission standards for gasoline passenger cars, has been designed and subjected to initial performance tests. A prevaporization-premixing combustion system was chosen as the most suitable system for the combustor. The detailed combustor design, including the use of ceramic components and fuel injectors, was pursued taking into account the allowable engine dimensions for vehicle installation. In the initial performance tests conducted at a combustor inlet temperature of 773K, a low NOx level was obtained that satisfied the steady state target at this temperature level.

A low emission combustor, which uses a prevaporization-premixing lean combustion system for the 100 kW automotive ceramic gas turbine (CGT), has been subjected to performance tests. Now a second combustor prototype (PPL-2), which incorporates improvements intended to overcome a flashback problem observed in an initial combustor prototype (PPL-1), is tested. The PPL-2 has been designed and built, so that it will substantially expand the stable combustion range. The improvement is accomplished by increasing the air distribution ratio in the lean combustion region to avoid flashback, providing a uniform flow velocity through the throat area and also by diluting the boundary layer so as to suppress flashback. Test results of the PPL-2 combustor show that it expands the flashback limit without affecting the blow out limit and is able to cover the stable combustion range need for the 100kW CGT.