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One of the key strategies to reduce CO2 emissions is to improve the efficiency of engines in order to diminish fuel consumption. A way to increase engine efficiency is to reduce the heat losses. Internal heat transfer in engines depends on combustion chamber conditions. Swirl is an important parameter for combustion that also changes in-cylinder variables relevant to heat transfer. In this work, influence of swirl on combustion chamber heat fluxes was investigated employing wall temperature data and a 0-D thermal model. Local wall temperatures were measured at various locations of the cylinder liner and the cylinder head using thermocouples. A sweep of swirl ratios was carried out at different engine operating conditions. It was observed that the effect of swirl effect was highly dependent on location and was more important near the center of the firedeck. Results from the 0-D thermal model were evaluated by comparing measured and predicted wall temperatures. Using a convenient arrangement of thermocouples and the 0-D thermal model, it was possible to calculate heat flux from combustion chamber to cylinder walls. By analyzing heat flux through the firedeck, an increase in heat losses between 4 and 12 % was observed for each unit that swirl number was increased. Results from the 0-D thermal model indicate that similar effects occur for other surfaces in the combustion chamber.

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HIGHLIGHTSOptoelectronic pyrometer provides similar results compared with a conventional method Lower injection pressure results in higher radiation Higher ambient temperature and higher in-cylinder gas density produce higher radiation Larger lift-off length reduces the soot volume fraction and the spectral intensity An increase on swirl number, load and CA50 provide a lower total radiation Lower values of EGR implies a decreased on radiation intensity KEYWORDSSoot; in-cylinder heat transfer; radiation; Optical pyrometer; ABSTRACTThe efficiency and CO 2 are one of the main concerns of automotive manufacturers.There are several strategies under investigation to solve this problem. In the present work, the research effort has been focused on improving knowledge of in-cylinder heat transfer and its impact on engine efficiency. In particular, soot radiation was studied since it can be considered a significant source of the efficiency losses in modern diesel engines. Considering previous studies, the portion of total chemical energy released during combustion lost due to radiation heat transfer varies widely from 0.5 up to 10%, depending on engine parameters and combustion process. Thus, the main objective of this work was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under different operating conditions in a completely controlled environment provided by an optical engine. Under these simplified conditions, two-color method was applied by using high speed imaging pyrometer with cameras (two dimensional results) and optoelectronic pyrometer (zero dimensional results). Once a detailed comparison between both diagnostics was performed, optoelectronic pyrometer was used to characterize radiant energy losses in a fully instrumented 4-cylinder direct-injection light-duty diesel engine. In particular swirl ratio, EGR and combustion phasing effects on radiation heat transfer were evaluated.

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NO x (oxides of nitrogen) emissions.A portion of the exhaust gases is recirculated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface. This adversely affects the combustion process, engine durability, and emissions. In this study, a 1-D model was developed to simulate soot deposition, soot removal, and condensation of several hydrocarbon (HC) species in a circular tube with turbulent gas flow at constant wall temperature. The circular tube, which makes up the computational domain in the model, represents a single channel from any EGR cooler geometry. The model takes into account soot particle deposition due to thermophoresis, diffusion, turbulent impaction, and gravitational drift. However, thermophoresis was found to be the most dominant deposition mechanism for boundary conditions at which EGR coolers typically operate. Soot removal was modeled by considering a force balance between the drag and van der Waals forces. A lognormal distribution of particles was assumed at the tube inlet. The evolution of the particle distribution in the bulk flow along the tube as well as the mass distribution in the deposit layer on the tube walls is predicted by the model. Condensation of six HC species between C 15 -C 24 alkanes was also modeled. Predictions made by the model are in reasonably good agreement with experimental data obtained from a laboratory reactor under the same boundary conditions. There are several assumptions and simplifications built into the model, which can be refined further to improve it.