Yoshinori Idota

Evaporation characteristics of fuel spray and low emissions in a lean premixed-prevaporization combustor for a 100 kW automotive ceramic gas turbine

A lean premixed-prevaporization combustor (PPL-1) for a 100 kW automotive ceramic gas turbine has been developed to meet the Japanese emission standards for passenger cars without using an aftertreatment system. The design of a fuel injector and a prevaporization-premixing tube (PP-tube) in the PPL-I combustor is a key subject for promotion of evaporation of fuel spray. The Sauter mean diameter and the non-evaporated mass fraction of fuel spray in the PP-tube were measured employing a phase Doppler particle analyzer varying inlet air temperature, air pressure, air velocity and swirl number. The evaporation of the fuel spray in the PP-tube was promoted by higher swirl number, air velocity, air temperature and increased atomization of the fuel injector, but was suppressed by higher air pressure and fuel properties such as distillation in high temperature. The characteristics of NO x , CO and HC emissions were measured with a combustor test rig and discussed influences of the evaporation characteristics of fuel spray. Results show that a mass fraction of non-evaporated fuel of less than 10% and lean fuel-air mixtures, i.e. having equivalence ratios from 0.15 to 0.5, reduce the PPL-I combustor emissions of NO x and CO.

Development of Dry Low-NOx Combustor for 300 kW Class Gas Turbine Applied to Co-Generation Systems

A 300 kWe class gas turbine which has a two-shaft and simple-cycle has been developed to apply to co-generation systems. The gas turbine engine is operated in the range of about 30% partial load to 100% load. The gas turbine combustor requires a wide range of stable operations and low NOx characteristics. A double staged lean premixed combustor, which has a primary combustion duct made of Si3N4 ceramics, was developed to meet NOx regulations of less than 80 ppm (corrected at 0% oxygen). The gas turbine with the combustor has demonstrated superior low-emission performance of around 40 ppm (corrected at 0% oxygen) of NOx, and more than 99.5% of combustion efficiency between 30% and 100% of engine load. Endurance testing has demonstrated stable high combustion performance over 3,000 hours in spite of a wide compressor inlet air temperature (CIT) range of 5 to 35 degree C.. While increasing the gas generator turbine speed, the flow rate of primary fuel was controlled to hold a constant equivalence ratio of around 0.5 in the CIT range of more than 15 C. The output power was also decreased while increasing the CIT, in order to keep a constant temperature at the turbine inlet. The NOx decreases in the CIT range of more than 15 C. On the other hand, the NOx increases in the CIT range of less than 15 C when the output power was kept a constant maximum power. As a result, NOx emission has a peak value of about 40 ppm at 15 C.Copyright

Ignition and Exhaust Emission Characteristics of Spray Combustion in a Pre-Chamber Type Vortex Combustor

The lean ignition limit, the lean blowout limit and the exhaust emission characteristics of spray combustion have been investigated experimentally using a pre-chamber type vortex combustor developed for a 300KW large-bus gas turbine engine. It has been verified that these depend on the spray characteristics of the fuel injector and the air flow pattern or the distribution of air in the chamber.Ignition succeeds through three processes. The first step is the formation of a flame kernel near the sparking ignitor, the second step is the propagation of the flame kernel into a flame holding region, and the last step is the formation of a rotating flame in that region. The lean blowout limit of the rotating flame depends on the air flow pattern in the pre-chamber when the air temperature in the combustor inlet is under 470K, while a constant fuel-air ratio of less than 0.001 is maintained at 470K and above. With no or a little secondary air, the NOx emission index does not increase in proportion to the fuel-air ratio, because both the gas temperature and residence time decrease due to the radiative heat loss caused by soot formation and reduction of a recirculation region in the main-chamber.These phenomena were evaluated with 3 dimensional numerical simulations taking account of spray combustion, soot formation, the extended-Zeldovich thermal NO formation and radiative heat loss.Copyright

A NEW FEEDBACK CARBURETOR WITH AIR JET COLLISION CONTROL

A new type closed loop A/F control carburetor has been developed. In the carburetor, an air jet, a by-pass stream of an intake air flow, is made to collide with a fuel flow to suppress the flow rate. Studies were made of the basic features of the method such as fuel controlling capability and the factors affecting it from phenomenological consideration and schlieren observation. For comparison, three types of carburetors were prepared for the combination of main and idle fuel circuits. In driving mode tests on a dynamometer, a new carburetor which employs the new method for the main fuel circuit, provides 30% lower emission level than an air bleed control carburetor. Higher controlling frequencies were obtained for the new carburetors. The high controllability of the air jet collision control method is attributable to the smaller fluctuation in both the controlling air and the spouting fuel.