By Bjorn Fehrm
December 02, 2016, ©. Leeham Co: We will now look at the combustor area in our series on modern turbofan engines. There is a lot of activity in this area, as it sets the level of pollution for the air transportation industry for some important combustion products.
We will also finish off the compressor part of our series by looking at the bleeding of cooling air for the engine and for servicing the aircraft with air conditioning and deicing air.
The amount of air which is tapped from compressor stages for cooling and other purposes can exceed 20% of the core flow (some of the flow paths are shown in Figure 1). At that level, it has a marked influence on the performance of the engine. Read more
November 18, 2016, ©. Leeham Co: In our series on modern turbofan airliner engines, we will now go deeper into the compressor part. Last week, we covered the fundamentals of compressors. As compressors and turbines use the same principles, we also covered the fundamental working principles of turbines.
We also described that compressors are temperamental parts, which can protest to wrong handling with violent “burps” (burst stalls with the combustion gases going out the front of the engine) or end up in a rotating stall where it simply stops working.
Turbines, on the other hand, are your robust companions. Aerodynamically they just work, albeit more or less efficiently dependent on what one asks them to do (mechanically it can be very different; we recently saw a turbine disintegrate with large consequences on an American Airlines Boeing 767 in Chicago). More on the turbines later.
In the GasTurb cross section of a two shaft turbofan in Figure 1, the engine has both an axial and a radial compressor. We will consider why engine designers combine these two for certain engine types. Read more
November 12, 2016, ©. Leeham Co: In our trip through a modern turbofan airliner engine and its technologies, we looked last week at the engine intake and the fan. We now continue with the compressor parts.
As compressors and turbines use the same principles (but in opposing ways), we will look at these principles this week and how their roles in the engine create their special characteristics.
As before, to make things concrete, we use a GasTurb simulation of a Rolls-Royce Trent XWB 84k engine to look at practical data when needed. As before, I have no specific knowledge about the engine and will not use any data outside what is public information.
The GasTurb cross section of a three-shaft turbofan is shown in Figure 1. We will examine the sections between station numbers (22) and (3) and (4) and (5) in the general discussion of compressors and turbines. We will then look at some data for common compressors. Read more
November 04, 2016, ©. Leeham Co: We will now start to go through a modern turbofan airliner engine and look at the technologies which are used and what are their technical challenges. We will start today with the engine intake and the fan.
To make things concrete, we will use a GasTurb simulation of a Rolls-Royce Trent XWB 84k engine. This will provide us with realistic example data for the different parts of the engine. I want to stress that all values are assumed as typical for such an engine. I have no specific knowledge of the Trent XWB and will not use any data outside what is public information.
The GasTurb cross section of a three-shaft turbofan is shown in Figure 1. We will use the station numbers in the figure to navigate the engine and the data from the simulation to understand modern airline engines and their typical data. Read more
October 28, 2016, ©. Leeham Co: Before we go into the details on the innards of airliner turbofans, we will look at some basics. We do that so that everyone is on the same page.
A turbofan engine generates thrust by pumping air out the back of the engine. This air has a higher speed than surrounding air. Air is actually quite heavy: it weighs 1.2kg per m3 at sea level. By kicking out air at an overspeed in relation to the aircraft, thrust is generated.
In a modern turbofan, the kicking gets done by the fan to 80-90% in the modern By Pass Ratio (BPR) 8-10 engines. A single aisle engine generating 10 tonnes of thrust throws around 350kg of air per second backwards at close to sound speed in a take-off situation. To drive the fan to do that, there is a lot of shaft horse-power needed, around 30,000hp.
These hp are generated by the core. The thermodynamic cycle to generate all these hp in a jet engine or turbofan core (we call both a gas turbine) is like the one in a normal car engine, Figure 1, with the difference that it is a continuous cycle.
We will now go through this cycle in steps. Read more
October 21, 2016, ©. Leeham Co: In our Corners on East bloc aeronautical industries, we could see that the hardest part to master in a new civilian airliner is the engine.
Both new airliners from Russia and China (Irkut MC-21 and COMAC C919) start their lives with Western engines.
Why is this so? What are the challenges that make engines harder to create than aircraft?
We will spend several Corners on the main reasons that airliner engines are harder to do than aircraft. Read more
October 14, 2016, ©. Leeham Co: In our Corners on East bloc aeronautical industries, we will now look at the role of the Research Institutes in Russian and Chinese civil aircraft engine development.
The Russian engine industry is organized similarly to the aircraft industry. It has a powerful research organization which has a much larger role than research organizations in the West.
A large part of fundamental design work and testing is done at the research institute and not at the design bureau level, Figure 1.
The Chinese organization of the engine industry is similar, the difference being that the research organizations are organized within the giant AVIC (Aviation Industry Corporation of China) grouping, rather than reporting to the state via a research organization path. Read more
October 07, 2016, ©. Leeham Co: In our Corners on East bloc aeronautical industries, we will now look at the Chinese civil aircraft engine industry.
The Chinese engine industry is closely modeled after the Chinese aircraft industry that we looked at last week. It is organized as divisions and later subsidiaries to the major aircraft companies. Contrary to the Chinese aircraft industry, it has had major problems in gaining the necessary know-how to start developing and producing its own designs.
The industry has built Soviet designs on license since the 1950s and only recently managed to present functional own designs, after many failures.
September 30, 2016, ©. Leeham Co: In our Corners on East bloc aeronautical industries, we will now look at the Chinese civil aircraft industry.
The Chinese aero industry has similarities with the Russian industry in its overall structure. From the start of the industry in the 1950s, it was structured after the Soviet model of research institutes, design bureaus and production companies.
The difference to the Soviet Union was that its own Chinese aircraft designs only started in the 1970s. Before that, the industry built Soviet designs on license and then modified versions of licensed designs.
The first own aircraft designs were presented in the 1980s with a focus on military designs for the first 20 years. Read more
September 23, 2016, ©. Leeham Co: In our Corners on East bloc aeronautical industries, we now look at the main Russian civil aircraft engine companies. As with the aircraft side, there is one overall Russian engine company since 2008, United Engine Corporation (UEC), Figure 1.
This is a state-owned holding which incorporates 80%of the gas turbine engine companies from the Soviet times, employing 80,000 people.
The aim is to coordinate and optimize Russia’s engineering and production resources around present and future gas turbine engines for Aeronautical, Naval and Stationary use.
Soviet and Russian engines have historically been named after their chief designer in the design bureau. We will now describe the main entities in UEC that work with airliner engines. Read more