Advantages of using a cooler bypass in the low-pressure exhaust gas recirculation line of a compression ignition diesel engine operating at cold conditions

Abstract

The low efficiency of the after-treatment systems during the cold start period of the internal combustion engines leads to excessive pollutant emissions levels. To reduce the nitrogen oxide emissions at these conditions, it could be necessary to use the high- and low-pressure exhaust gas recirculation strategies, even operating at low temperatures. This article evaluates the impact of using a low-pressure exhaust gas recirculation cooler bypass in a Euro 6 turbocharged diesel engine running under cold conditions (–7 °C). A new compact line fitted with a bypass system for the cooler is used with the aim of accelerating the engine warm-up process as compared to the original low-pressure exhaust gas recirculation line. The system is evaluated following two strategies, first performing exhaust gas recirculation without bypass and then performing exhaust gas recirculation bypassing the cooler. The results show that the activation the low-pressure exhaust gas recirculation from the engine cold start leads to a significant nitrogen oxide emissions reduction. Moreover, the bypass activation leads to increase the engine intake temperature, reducing the engine warm-up time and the CO emissions due to better combustion efficiency. However, the activation of the low-pressure exhaust gas recirculation at low temperatures could produce condensation and fouling deposits on the engine components affecting their life span. These phenomena are visualized using endoscope cameras in order to identify the condensation time and the final conditions of the elements. In addition, a chemical analysis of some condensates collected during the experiments and a comparison versus other species found in the literature is presented.

Parametric study of the impact of EGR and fuel properties on diesel engine performance using a predictive thermodynamic model

“…Finally, the use of uncooled lowpressure EGR is useful even during engine cold start operation to decrease NO, while after-treatment systems are disabled, and to accelerate the engine warm-up period. 40 However, uncooled high-pressure EGR seems to be preferable under cold conditions to avoid water condensation and carbon emissions. 41 This short literature survey thus highlights that efforts undertaken in the field of quasi-dimensional modeling include the development of fuel spray penetration and mixture formation sub-models as well as the implementation of different approaches to model the combustion process (from the imposed HRR to the recent use of kinetic schemes), so-enabling predicting engine performance and/or studying the impact of EGR.…”

“…Finally, the use of uncooled low-pressure EGR is useful even during engine cold start operation to decrease NO, while after-treatment systems are disabled, and to accelerate the engine warm-up period. 40 However, uncooled high-pressure EGR seems to be preferable under cold conditions to avoid water condensation and carbon emissions. 41…”

Fuel consumption and aftertreatment thermal management synergy in compression ignition engines at variable altitude and ambient temperature

“…8 This can be partially balanced using a LP-EGR cooler by-pass. 9 Luja´n et al 5 also analysed the impact of very low ambient temperature on the CO and HC emissions of a diesel engine running WLTC tests. The engine was equipped with high pressure (HP) and LP-EGR operating with serial calibration.…”

EGR cylinder deactivation strategy to accelerate the warm-up and restart processes in a Diesel engine operating at cold conditions

“…8,9 In this sense, it is proved that accelerating the warm-up process and increasing the engine temperatures can provide benefits such as HC and CO emissions reduction, combustion noise control and engine stability improvement after the cold start, besides of the possibility of implement different and enhanced warm-up and EGR calibration strategies. [10][11][12] In the recent years, different strategies have been developed to improve the thermal efficiency of the ICE and accelerate its thermal transient. Some of these strategies are the cylinder cutout 13 or the variable valve timing (VVT), 14,15 which can be combined with novel strategies as the cylinder ventilation.…”