The aircrafts are responsible for emitting several types of pollutants, especially the pollutants in the form of NOX, CO2, CO, UHC, SOX and Particulate Matter PM (smoke/soot). The impact of aviation emissions on the global is well known, where these emissions modify the chemical and microphysical properties of the atmosphere resulting in changes of earth’s climate system, which can ultimate in critical changes in our planet fragile ecosystem, also the pollutants produced by aircraft engines cause many health problems. This is why the International Civil Aviation Organisation (ICAO) is seriously seeking to control the emission levels by issuing new standards during the successive meetings of the Committee on Aviation Environmental Protection CAEP (CAEP/01 in 1986, CAEP/2, CAEP/4, CAEP/6, CAEP/8, etc). The new regulations include more stringent standards aimed to reduce emission levels, this led to increased interest in low emission technologies. In this paper, a comprehensive review of low emissions combustion technologies for modern aero gas turbines is represented. The current low emission technologies include the high Technologies Readiness Level (TRL) including RQL, TAPS, DAC and LDI. Also, there are advanced technologies at lower TRL including LPP, ASC and VGC.

DP steels were extensively used in the vehicles industry due to its extraordinary combined properties of strength, ductility, formability and weldability which contributed great significance in reducing strength to weight ratio and CO2 emission. High strength steel i.e. DP steels (3 different grades) were experimentally investigated and thermophysically simulated using Gleeble 3500 simulator to determine softening and hardening in heat affected zone. Samples were heated to different peak temperatures (1350 °C, 950 °C, 775 °C and 650 °C), two cooling time (t8.5/5 = 5 s and 30 s) and Rykalin 2D model were selected. The hardness and microstructure of the specimens were tested and analysed. For longer cooling time (t8.5/5= 30 s), we observed that softening occurs in all grade of investigated DP steels to all sub-regions. But for shorter cooling time i.e. t8.5/5= 5 s the softening is higher in intercritical HAZ compared to other sub-regions for all the types of DP steel with short cooling time (t8.5/5 = 5 s). However, the hardening zone in the CGHAZ occurs when Tmax is 1350 ºC for DP600, DP800 & DP1000 steels but it is more prominent in DP800 as compared to others two steel grade.

Welding is the most common technique used to produce different products. High strength steels are the most important steels used nowadays, these steels have excellent properties such as high strength and good ductility. They derive these properties from their special microstructures which are more versatile and complex compared to other steels. The welding of new steels with ultrahigh tensile strength is a great challenge, not like the other metals where using of the conventional welding methods is suitable, this is why it is very important to select the appropriate welding method with the exact welding parameters which can ensure good welding without losing the excellent mechanical properties of these steels. This scientific paper represents a detailed literature overview about all the aspect related to the weldability of HSSs.