Search Results

Despite the development in NOx aftertreatment for Diesel engines, EGR is a cost-effective solution to fulfill current and future emission regulations. There is a wide bibliography discussing the global effects of EGR on combustion and emissions. However, little has been published concerning the effects of the unsuitable EGR and air distribution among cylinders. Since current HSDI engines operate with EGR rates as high as 50% the effect of the unequal EGR distribution becomes important. In addition, cylinder-to-cylinder charge dispersion becomes a critical aspect on the control of low temperature combustion systems. In concordance with the aspects outlined before, the aim of this paper is to study the effects of the EGR cylinder to cylinder distribution on the engine performance and emissions. To cope with this objective, experiments have been conducted in a HSDI engine with two different EGR systems.

In order to further reduce NOx emissions in increasing HP EGR cooler performance, several OEMs have decided to use a secondary cooling loop dedicated to bring cold water (around 35°C) to the HP EGR heat exchanger. Nevertheless, strongly cooled EGR gases can condensate in the cooler-producing acidic liquids which can corrode some parts in the loop. It is therefore necessary to define EGR components compatible with such kind of environment and constraints. Testing was performed on a 2.0-liter EU4 diesel engine, using a large panel of current fuels including neat biodiesels from soybean, rapeseed or palm, as well as low and high sulfur petroleum-based diesels. In order to cover all existing cycle conditions, the HP EGR is cooled from 20°C to 90°C independently from the engine coolant circuit.

This paper shows the potential of a multicalibration approach for reducing fuel consumption while keeping pollutant immissions. The paper demonstrates that the current engine control approach with a single fixed calibration involves important fuel penalties in areas with low vehicle densities where local pollution is not an issue, while the NOx emissions in urban areas are usually too high to fulfill air quality standards. The proposed strategy is based on using information about the vehicle location and the NOx concentrations in the ambient to choose a suitable calibration amongst a set of possibilities. To assess the potential of such a strategy experimental tests have been done with a state-of-art turbocharged Diesel engine. First, a design of experiments is used to obtain three different calibrations.

Low pressure exhaust gases recirculation (LP-EGR) is becoming a state-of-the-art technique for Nitrogen oxides (NOx) reduction in compression ignited (CI) engines. However, despite the pollutant reduction benefits, LP-EGR suffers from strong non-linearities and delays which are difficult to handle, resulting in reduced engine performance under certain conditions. Measurement and observation of oxygen concentration at the intake have been a research topic over the past few years, and it may be critical for transition phases (from low pressure to high pressure EGR). Here, an adequate selection of models and sensors is essential to obtain a precise and fast measurement for control purposes. The present paper analyses different sensor configurations, with oxygen concentration measurements at the intake and exhaust manifold and combines observation techniques with sensor models to determine the potential of each configuration.

Fuel-to-air ratio stimulation, also called λ cycling or λ modulation, is a natural consequence of controlling fuel-to-air ratio in closed-loop with a switch-type λ-sensor. Nowadays, wideband λ-sensors are broadly extended and fuel-to-air ratio stimulation is an additional option that can or not be implemented in the control strategies to improve TWC conversion efficiency through the increase of the catalyst activity. The present work focus on the suitability of applying fuel-to-air ratio stimulation in a turbocharged GDI engine equipped with a close-coupled TWC. In particular, the influence of the main parameters such as stimulation amplitude and frequency on tailpipe emissions at steady-state conditions is assessed. The potential of λ cycling in order to reduce pollutant emissions in the face of fuel-to-air ratio disturbances has also been evaluated. Results show how a proper λ modulation decreases NOx emissions at lean conditions.

Testing was performed on a 2.0 liter diesel engine with high pressure (HP) and low pressure (LP) EGR, using standard European low sulfur diesel as well as fatty acid methyl ester (FAME) biodiesel fuels produced from soy, rapeseed and palm feedstock, both neat and blended with 50% standard diesel. In the HP EGR configuration, fuel injection, air flow and EGR rate were adapted to achieve the same engine load and NOx emissions for all fuels at the selected test points. Higher brake specific fuel consumption and lower smoke emissions were observed for the biodiesels compared to the standard diesel. In the LP EGR configuration, large reductions in NOx and smoke were observed for all fuels compared to HP EGR. In addition, water condensed in the charge air cooler at coolant temperatures below 30°C. This condensate was collected and analyzed, finding similar volumes and acidity for condensates from all the diesel and biodiesel fuels.