Value Of Digital EGT Gauge For Precision Engine Monitoring

During World War II and in response to the war ministry’s directives, aircraft manufacturers had to constantly try and improve the engine power as well as the range of their aircraft – especially the bombers. The pressure to increase power and range happened with both – the allied forces and Nazi Germany. So how does the presence of an EGT probe and the Exhaust Gas Temperature display unit (EGT) help improve aircraft power, range and assist in precision engine monitoring?

This is how it worked:

If fuel is not efficiently burnt, it passes out of the engine and into the exhaust. Such fuel laden exhaust is termed “rich”. On the other hand, if there is more air-to-fuel in the exhaust, it is termed as “lean”. The aircraft engineers noticed a correlation between the exhaust gas temperatures and rich or lean exhaust.

Further experiments indicated that the maximum power in an aircraft is developed when the fuel-air mixture is set to an EGT reading of Peak EGT – 100 o F. The engineers found that this was achieved with a fuel-air ratio of roughly .083. At this setting, the aircraft consumed roughly 25% more fuel but at the same time, it also produced the maximum possible power which during the World War II made a lot of difference especially when escaping enemy aircraft or enemy fire. That said, the first commercial EGT display wasn’t available until the mid-nineties when it was created by an engineer named Al Hundere. Thus was born the EGT display – a way for the pilots to achieve the best possible results during flight.

At a more practical level, having an EGT display meant the pilot knew if there was unburned fuel in the exhaust gas. Such a situation mean the fuel-to-air ratio was inefficient. Conversely, he would also know if there was too much air in the exhaust resulting in the aircraft being underpowered because less fuel in the mixture meant less energy output.

The initial EGT displays were Aircraft Gauges that had a series of markings or ticks each set 25°F apart. The pilot had to note where the needle peaked and would richen the mixture until the needle dropped to the desired temperature. There was no way for the pilot to determine the absolute value of EGT.

Everything changed when J.P. Instruments introduced its first dual display Slimline Pressure Gauge for precision engine monitoring – the EDM-700. The EDM 700 featured bar graph and a digital readout and so, for the first time the pilots had an accurate picture of fuel-air mixture. High EGTs informed the pilot that a lot of fuel was simply passing through the engine and out of the exhaust without very being utilised.

The digital EGT display numbers are a direct product of the aircraft engine combustion process. Understanding how the digital EGT display numbers relate to fuel consumption, aircraft range and endurance, engine power for fuel management and power plant management is absolutely essential for a safe and successful flight. Obviously, if you own the aircraft and are paying for its use and maintenance, you will know right away how well you understand the EGT readouts on your digital EGT gauge. The digital EGT gauge is an invaluable tool to precision engine monitoring.