Engine-out Carbon Monoxide Research Articles

3D CFD simulation of a CI engine converted to SI natural gas operation using the G-equation

The conversion of heavy-duty CI engines to natural gas (NG) SI operation have the potential to increase the use of NG in the transportation sector in the United States. More, the increased turbulence of a bowl-in-piston combustion chamber can increase the flame speed under more efficient lean conditions. The main objective of this study was to investigate if a 3D G-equation-based RANS simulation (i.e., reasonable computational costs and running times) can predict the efficiency and emissions of such converted engine, for various NG compositions and operating conditions. The model was validated with experimental data from a single-cylinder CI research engine that replaced the fuel injector with a spark plug and fumigated NG inside the intake manifold using a low-pressure gas injector. Using a unique set of model tuning parameters, the model was able to qualitatively predict the effect of NG composition on engine performance and emissions over a range of operating conditions that changed spark timing, equivalence ratio, and engine speed. The model also captured the double-peak heat release rate seen at advanced spark timing in the experiments. The results showed that a lower methane number (MN) increased peak pressure and indicated mean effective pressure. Higher H/C ratio advanced combustion phasing. More, higher MN lowered nitrogen oxides but increased unburned hydrocarbons emissions. However, while a lower MN increased carbon monoxide (CO) production during the combustion process, there was no clear trend for engine-out CO emissions. Overall, the predicted gas composition effects on engine efficiency and emissions were relatively small, at least for the range of operating conditions investigated here. However, the results suggest that the 3D CFD model described here is suitable for combustion phenomena analysis such the flame behavior in a bowl-in-piston combustion chamber.

Emission Characteristics of a Natural Gas Engine Operating in Lean-Burn and Stoichiometric Modes

AbstractTo comply with the stringent Euro VI emission standards, two techniques have been proposed for natural gas engines, namely, lean-burn combustion with oxidation catalyst (OC) and stoichiometric combustion with three-way catalyst (TWC). In this paper, comparisons are drawn between the two techniques in terms of carbon monoxide (CO), nitrogen oxides (NOx), and methane (CH4) emissions and fuel economy. The results indicated that the postcatalyst CO emissions of lean-burn combustion with OC are lower, whereas the postcatalyst NOx and CH4 emissions are higher than those of stoichiometric combustion with TWC. This can be explained by the combined effects of lower engine-out CO emissions and higher engine-out NOx and CH4 emissions as well as lower overall conversion efficiency for all emissions with the adoption of lean-burn combustion with OC. Thus, it can be concluded that although the fuel economy of stoichiometric combustion with TWC is inferior to lean-burn combustion with OC, it is still considered ...

Experimental investigation of diesel and biodiesel post injections during active diesel particulate filter regenerations

The purpose of this study is to investigate the common-rail diesel engine and aftertreatment system behaviors during active diesel particulate filter (DPF) regenerations with pure biodiesel and conventional diesel fuels. The experiments were conducted on a medium-duty diesel engine equipped with a high pressure common-rail fuel injection system. The comparative effects of post start of injection (SOI) timing, post fuel injection rate, and the number of post injections, on the engine behaviors including exhaust emissions (total hydrocarbon (THC), carbon monoxide (CO), and oxides of nitrogen (NOx)), exhaust gas temperatures, torque output, and the THC and CO conversion efficiencies inside a diesel oxidation catalyst (DOC), are presented and discussed. Experimental results show that, for both fuels, the engine-out THC emissions at late post injection timings are significantly higher than that at early post injection timings, while the engine-out CO emissions reach the peak values in mid phase of power strokes and the engine-out NOx emissions can be reduced with a late-cycle post injection. Engine torque output and cylinder-out gas temperatures can be promoted obviously with an early post injection. Post injection rate is the dominant factor influencing the exhaust emissions at fixed post SOI timings. Regarding the main differences between the two fuels, substantially lower engine-out THC and CO emissions can be observed from late post injection with biodiesel than those with diesel. The addition of an early post injection to a late post injection has little effect on the engine-out THC emissions, but can lead to higher engine-out CO emissions and higher cylinder-out gas temperatures. Furthermore, substituting diesel with biodiesel in the engine can lower the cylinder-out gas temperature, the engine torque disturbance, and the THC and CO conversion efficiencies inside the DOC.

Predictions of the effects of piston-liner crevices on flow motion and emissions in three-dimensional diesel engine simulations

Computational fluid dynamics predictions of the flow field and pollutant emissions in a high-speed direct-injection diesel engine operating at high load and rated speed are presented. Piston-liner crevice flows during the expansion stroke can give rise to vortex motions whose characteristics depend on the piston crevice configuration. Both a realistic and a simplified crevice volume that consists of a neck area and a reservoir to keep the surface—volume ratio realistic are considered. In the simplified crevice approach, with moderate intensity of the crevice flow, the vortex enhances mixing and engine-out carbon monoxide (CO) emissions are reduced. However, when the crevice flow intensity is above a certain level, a strong tumble motion is created in the bulk mixture in the squish area, which isolates a region of high CO concentration and prevents oxidation. The results also show that proper timing of the crevice flow into the combustion chamber lowers the mixture temperature and reduces nitrogen oxide emissions. Calculations with a realistic crevice flow geometry and a crevice flow submodel also predict squish region vortex motion.

The impact of biodiesel blend ratio on vehicle performance and emissions

Biodiesel is synthesized via the transesterification of triglycerides contained within vegetable, animal, or waste oils. First-generation biofuels are not the solution to global transport energy needs; however, biodiesel does have a role to play in reducing greenhouse gas emissions from the transport sector, so long as necessary production can be achieved in a sustainable manner without negative impact on plant and animal biodiversity. The biodiesel content within diesel sold to consumers is set to increase in the future, with implications on vehicle fuel consumption, emissions, and base engine durability. This study examines the effects of increasing the biodiesel blend ratio on the performance and emissions of a production vehicle equipped with a common-rail direct-injection diesel engine, evaluated on a chassis rolls dynamometer, at various ambient temperatures. Results obtained show that reductions in engine-out carbon monoxide and hydrocarbon emissions do not always translate to lower tailpipe emissions as reduced exhaust gas temperatures at higher blend ratios lead to reduced catalyst conversion efficiencies and higher total cycle emissions. Catalyst conversion efficiencies for carbon monoxide and hydrocarbons over the New European Drive Cycle (NEDC) are reduced by 9–19 per cent (depending on the ambient temperature) for a 50:50 blend (B50) compared with the petroleum diesel (B0) baseline. Increasing the blend ratio caused a linear decrease in the vehicle's maximum tractive force. This reduction was of the order of 5 per cent for a B50 blend at low vehicle speeds and 6–10 per cent at higher speeds, which is greater than would be expected on the basis of the differences in calorific values. Over the NEDC, the fuel consumption was found to increase with increasing blend ratio.