|Trials||up to 900|
|Trials||up to 13000|
Experimental conversion of an early production Tu-154, used as a testbed for cryogenic fuel system. First in the World aircraft of this type.
Search for alternative fuel technologies was initiated by the Soviet Government in late 1970s during the oil crisis. Two potential fuels were considered: liquid hydrogen (LH) and liquid natural gas (LNG).
The major modification of the fuel moved new engine development into a top priority. Kuznetsov Engine Design Bureau performed conversion of the series NK-8 into NK-88. New powerplant could be switched from cryogenic to conventional fuel.
Trials were performed on the early production Tu-154 CCCP-85035, "owned" by the Tupolev design bureau. New engine was fitted at the starboard position, while two other engines were normal NK-8. Only minor changes were done to the air intake to match NK-88 airflow requirements. The only other visible modification was a small extra fin mounted on the top of the tail. This fin was actually a part of new fuel system.
The interior of the aircraft changed dramatically. Rear part of the passenger cabin was occupied by large pressurized dewar tank. New centrifugal pumps with higher than normal heat exchange efficiency were installed. Unusual fuel required also new alarm and safety systems to be used.
One of the trials problems was absence of corresponding refueling facilities at any airport in the USSR or in the world. Zhukovskij experimental airfield was chosen. Cryogenic gas storages were built, but aircraft fueling was performed from specially equipped trucks (for at a time). For safety reasons, all procedures were remotely controlled.
First flight was performed on April 18, 1988 by crew under command of Andrei Talalakin. Liquid hydrogen fed engine was tested at altitudes up to 7000m and speeds up to 900km/h. In-flight starts and failures of the experimental engine were simulated, fire extinguishing system also was tried.
Liquid Hydrogen (LH) program was cut down to only five flights. Decision was made not to proceed with this type of fuel:
Natural gas appeared more promising from the availability and cost point, but conversion of the fuel system turned to be more complex task than for Liquid Hydrogen. The density of the Liquid Natural Gas (LNG) is just 1/6 of the LH. More efficient pumps were required to supply enough fuel to run the engine. Another problem was boiling of the LNG, causing large fluctuations in the fuel flow. Finally problem was solved by evaporating the liquid and feeding the engine pumps with gas at -70°C (boiling temperature for LNG is -160°C).
In-flight trials began on January 18, 1989 and continued for five years (more than 80 flights). This time all aspects of flight were evaluated up to 13000m of altitude. Among the tests was in-flight switching of the engine from cryogenic fuel to kerosene and back. This procedure took just five seconds.
Plans to convert one Tu-154B into operational airliner with dual fuel (Tu-156 were frozen under pressure of enormous political and economical problems in Russia in the 1990s. Fir a while, future of the program was uncertain.
In the beginning of new millennia economical situation in Russia stabilized, and interest in the cryogenic fuels was re-ignited. Financing of new project (Tu-204K) began in 2002 with approximately 50% coming from the State Budget. This time the Tu-156 program is considered as an intermediate R&D phase. Special interest for those aircraft were expressed by GAZPROM: they may be used effectively at the Russian Far North and Far East, where jet fuel is often scarce but gas is plentiful.
в развитие отечественного двигателестроения
|Created February 16, 2002||Back to|