Search Results

The oxidations of Crapped diesel soots containing catalytic metals such as Ca, Ba, Fe, or Ni were characterized through thermogravimetric analysis with a thermobalance. Soot particles were generated by a single cylinder IDI diesel engine with metallic fuel additives. A two-stage oxidation process was observed with the metalcontalning soots. It was found that the first stage of oxidation is catalytically promoted by metal additives resulting in an enhanced reaction rate and a reduced activation energy. Soot reduction in the rapid first stage increases with increases in metal content. Soots containing Ba and Ca are oxidized most rapidly due to the larger reduction during the first stage. The second stage of oxidation is also slightly promoted by metal addition. The ignition temperature of the collected soot is substantially reduced by the metal additives.

Experiments on a large number of soluble fuel additives were systematically conducted for diesel soot reduction. It was found that Ca and Ba were the most effective soot suppressors. The main determinants of soot reduction were: the metal mol-content of the fuel, the excess air factor, and the gas turbulence in the combustion chamber. The soot reduction ratio was expressed by an exponential function of the metal mol-content in the fuel, depending on the metal but independent of the metal compound. A rise in excess air factor or gas turbulence increased the value of a coefficient in the function, resulting in larger reductions in soot with the fuel additives. High-speed soot sampling from the cylinder showed that with the metal additive, the soot concentration in the combustion chamber was substantially reduced during the whole period of combustion. It is thought that the additive acts as a catalyst not only to improve soot oxidation but also to suppress soot formation.

To reduce NOx emissions from diesel engines, the urea-SCR (selective catalytic reduction) system has been introduced commercially. In urea-SCR, the freezing point of the urea aqueous solution, the deoxidizer, is −11°C, and the handling of the deoxidizer under cold weather conditions is a problem. Further, the ammonia escape from the catalyst and the generation of N2O emissions are also problems. To overcome these disadvantages of the urea-SCR system, the addition of a hydrocarbon deoxidizer has attracted attention. In this paper, a micro-reactor SCR system was developed and attached to the exhaust pipe of a single cylinder diesel engine. With the micro-reactor, the catalyst temperature, quantity of deoxidizer, and the space velocity can be controlled, and it is possible to use it with gas and liquid phase deoxidizers. The catalyst used in the tests reported here is Ag(1wt%)-γAl2O3.

To meet the future emission targets for Diesel engines, one trend is the use of Catalyzed Diesel Particulate Filters (CDPF). Catalyzing the filter, however, alters filter behavior. In particular, alteration in filter permeability imparts a significant change in the filter's performance. To understand the impact of the catalyst coating on a DPF, engine tests have been conducted to measure the pressure drop across DPFs with different catalyst coatings, cell densities, and soot loadings. The tests were performed over a range of engine speeds and loads, with a corresponding range in exhaust flow rates and temperatures. A pressure drop model based on previous work for uncatalyzed filters has been modified and validated for CDPFs. To achieve optimum design for DPF's, a parametric study comparing the influence of catalyst, cell density, wall thickness, filter length and diameter was done.

Diesel combustion and emissions with four kinds of oxygenated agents as main fuels were investigated. Significant improvements in smoke, particulate matter, NOx, THC, and thermal efficiency were simultaneously realized with the oxygenates, and engine noise was also remarkably reduced for the oxygenates with higher ignitability. The improvements in the exhaust emissions and the thermal efficiency depended almost entirely on the oxygen content in the fuels regardless of the oxygenate to diesel fuel blend ratios and type of oxygenate. The unburned THC emission and odor intensity under starting condition with an oxygenate were also much lower than with conventional diesel fuel.

Diesel soot suppression effects of catalytic fuel additives for a range of fuels with different properties were investigated with calcium naphthenate. A single cylinder DI diesel engine and a thermobalance were used to determine the soot reduction and its mechanism for seven kinds of fuels. Experimental results showed that the catalytic effect of the fuel additive was different for the different fuels, and could be described by a parameter considering cetane number and kinematic viscosity. The fuel additives reduced soot more effectively for fuels with higher cetane number and lower kinematic viscosity. This result was explained by soot oxidation characteristics for the different fuels. Oxidation of soot with the metallic additive proceeds in two stages: stage I, a very rapid oxidation stage; and stage II, a following slow or ordinary oxidation stage.