The effect of the initial coolant temperature of an EGR equipped engine on nitrogen oxide emissions during a cold start FTP cycle

The purpose of this study was to examine the effects of the initial coolant temperature on oxides of nitrogen (NOx) emissions during a cold start test of a heavy duty diesel engine equipped with exhaust gas recirculation (EGR) and to compare the results to an engine that was not equipped with EGR. Two heavy duty diesel engines, a model year 2004 production Cummins ISX and a John Deere Tier 3 compliant test engine were examined in an engine emissions testing laboratory designed according to the Code of Federal Regulations (CFR) Title 40 Part 1065-Engine Testing Procedures. The Cummins engine was equipped with EGR while the John Deere engine was not. The Cummins engine was tested in both hot and cold start Federal Test Procedure (FTP) cycles while the John Deere engine was tested in both hot and cold start Non-Road Transient Cycle (NRTC) tests. For a cold start test to be valid, the engine oil and coolant temperature had to be maintained at temperatures between 20 and 30°C prior to the start of the cold test. It was found that the cold start tests of the Cummins engine equipped with EGR that started with an initial coolant temperature closer to 30°C produced NOx emissions that were less than the NOx emissions produced from a cold start test whose initial coolant temperature was closer to 20°C. The NOx emissions and the initial coolant temperature showed the greatest negative correlation around the time the engine's thermostat opened. The correlation was the strongest around the time the thermostat opened because the EGR was activated around that same time. A 100 second window that focused on the time at which EGR was initiated during the test was examined. The correlations between the initial coolant temperature and the NOx emissions over 27 cold start FTP cycles for two different fuels from the 100 second window were -41.2% and -46.8% for the Cummins engine. The correlation between the initial coolant temperature and NOx emissions from the same 100 second window of the John Deere engine was 1.75%. The EGR valve was initially activated according to the coolant temperature in the Cummins engine. Although the coolant temperatures are slightly different at the beginning of each test, the coolant temperature during all the cold start tests of the Cummins engine increased at the same rate. The tests that started out with a warmer coolant temperature reached a thermostat opening temperature earlier in the test and therefore EGR was activated sooner which lead to a greater amount of time in the test for the effect of EGR to reduce NOx emissions. The hot start FTP cycles of Cummins and the hot and cold start NRTC tests of the John Deere engine showed a weak correlation between their initial coolant temperatures and NOx emissions. It was concluded that if an engine that utilizes EGR is tested in a cold start FTP cycle, the initial coolant temperature has a strong effect on the cycle NOx emissions.