egr solutions

WHAT IS EGR?

A widely adopted route to reduce NOx emissions is Exhaust Gas Recirculation (EGR). This involves recirculating a controllable proportion of the engine's exhaust back into the intake air. A valve is usually used to control the flow of gas, and the valve may be closed completely if required.

The substitution of burnt gas (which takes no further part in combustion) for oxygen rich air reduces the proportion of the cylinder contents available for combustion. This causes a correspondingly lower heat release and peak cylinder temperature, and reduces the formation of NOx. The presence of an inert gas in the cylinder further limits the peak temperature (more than throttling alone in a spark ignition engine).

The gas to be recirculated may also be passed through an EGR cooler, which is usually of the air/water type. This reduces the temperature of the gas, which reduces the cylinder charge temperature when EGR is employed. This has two benefits- the reduction of charge temperature results in lower peak temperature, and the greater density of cooled EGR gas allows a higher proportion of EGR to be used. On a diesel engine the recirculated fraction may be as high as 50% under some operating conditions.

HOW EGR WORKS?

The EGR theory works by sending a small part of inactive gas exhaust back into a vehicle's cylinders, hence eject negligible toxins into the environment. This reduces the heat of combustion yet the same amount of pressure is still applied to this piston while reducing the amount of excess oxygen prior to combustion. A few studies conducted on diesel engines demonstrate that the portion of nitrous oxide gas emissions is definitely reduced through the use of EGR, however concentrations of smoke density can actually increase. Thus there seem to be pluses and minuses depending on what's important to you in your specific vehicle

Usually, an engine recirculates exhaust gas by piping it from the exhaust manifold to the inlet manifold. This design is called external EGR. A control valve (EGR Valve) within the circuit regulates and times the gas flow. Some engines incorporate a camshaft with relatively large overlap during which both the intake valve and the exhaust valve are open, thus trapping exhaust gas within the cylinder by not fully expelling it during the exhaust stroke.