That's not the main purpose of the EGR valve. It's to reduce NOx. From Wiki.
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In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.[1] Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates (though at some loss of engine efficiency).[2] Gasses re-introduced from EGR systems will also contain near equilibrium concentrations of NOx and CO; the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on a time average. Most modern engines now require exhaust gas recirculation to meet emissions standards
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Petrol engines have EGR valves as well.
From Autospeed...
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UK researchers working for the engine component manufacturer Mahle conducted testing on a 2-litre, 4-valves-per-cylinder, direct injected, turbocharged and intercooled petrol engine. The EGR system was of the external type and used a cooler that reduced exhaust gas temp to just 20 degrees C. The system added the cooled exhaust gas well ahead of the turbo compressor (note: so apparently not after the throttle body).
When running at high power outputs, the engine used a modest amount of fuel enrichment and a large amount of cooled EGR to achieve Specific Fuel Consumption up to 16 per cent better than with fuel enrichment alone. Under the same operating conditions, the reduction in NOx was about 30 per cent, the reduction in CO was 70 per cent, and HC was 80 per cent.
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Last edited by RoyMacDonald; Jan 18th, 2015 at 20:17.
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