Ewa A. Bardasz

Investigations of the Interactions between Lubricant-derived Species and Aftertreatment Systems on a State-of-the-Art Heavy Duty Diesel Engine

The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems. Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine. The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run. Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface. Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices. This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.

Effects of Lubricant Derived Chemistries on Performance of the Catalyzed Diesel Particulate Filters

Forthcoming on-highway 2005/2007 European and North American emission regulations will require modern diesel engines to be equipped with Diesel Particulate Filters (DPF) capable of trapping up to 99% of the exhaust particulate matter. Since diesel particulates (soot) accumulate in the filter over time, the overall system needs to be regenerated by attaining the ignition temperature of soot, which in the presence of oxygen is >600 °C. Catalyzed DPFs regenerate at temperatures as low as ∼300 °C. One of the major issues facing OEMs, aftertreatment system manufacturers, and lubricant formulators is the potential effects of the lubricant-derived ash deposits and their impact on a pressure increase across filters, as well as overall filter performance and its service characteristics. In the present study, several lubricant-formulating additive variables, metal detergent type, antiwear additive (ZDP) type and level, the presence of boron as well as the effect of noble metal concentration in catalyzed DPF were examined. The paper explores ramifications of these formulation variables, especially the effects of lubricant chemistry, on DPF balance point temperature, ash deposits distribution and recovery. Findings identify the impact of lubricant derived species on soot combustion, ash type and presence of volatile components within the filter deposits.

Engine oil effects on friction and wear using 2.2L direct injection diesel engine components for bench testing part 2- tribology bench test results and surface analyses

The effects of lubricating oil on friction and wear were investigated using light-duty 2.2L compression ignition direct injection (CIDI) engine components for bench testing. A matrix of test oils varying in viscosity, friction modifier level and chemistry, and base stock chemistry (mineral and synthetic) was investigated. Among all engine oils used for bench tests, the engine oil containing MoDTC friction modifier showed the lowest friction compared with the engine oils with organic friction modifier or the other engine oils without any friction modifier. Mineral-based engine oils of the same viscosity grade and oil formulation had slightly lower friction than synthetic-based engine oils. In the comparison of wear on cylinder bores lubricated with the same viscosity of lubricant, the lubricant containing the MoDTC friction modifier had the lowest wear depth, probably because of a wear-resistant reaction film formed by the reaction of sulfur from ZnDTP (Zinc Dialkyl Dithiophosphate) and MoDTC. The wear depth of the engine oil without any friction modifier was the highest among all lubricants tested. With MoDTC in the engine oil, the wear depths for all tested piston rings were lower than those operating in the absence of MoDTC. This might be caused by a synergistic wear-resistant film formation (both MoS 2 and polyphosphates formed) on both cast iron bores and piston rings as evidenced by EDX and XPS surface analyses. Surface analyses were conducted to help understand the surface mechanisms responsible for friction reduction and the impact of engine materials and additives on wear.

The Impact of Lubricant and Fuel Derived Sulfur Species on Efficiency and Durability of Diesel NOx Adsorbers

Global emission legislations for diesel engines are becoming increasingly stringent. While the exhaust gas composition requirements for prior iterations of emission legislation could be met with improvements in the engines combustion process, the next issue of European, North American and Japanese emission limits greater than 2005 will require more rigorous measures, mainly employment of exhaust gas aftertreatment systems. As a result, many American diesel OEMs are considering NOx adsorbers as a means to achieve 2007+ emission standards. Since the efficacy of a NOx adsorber over its lifetime is significantly affected by \sulfur (sulfur poisoning), forthcoming reductions in diesel fuel sulfur (down to 15 ppm), have raised industry concerns regarding compatibility and possible poisoning effects of sulfur from the lubricant. Since relatively little is known about the interaction between lubricant derived sulfur and NOx adsorbers, a joint technical program was conducted using a Cummins 5.9L engine and NOx adsorbers supplied by Delphi. Fuel sulfur was kept constant (2ppm) while the effects of high (0.6%) and ultra low (0.003%) S containing lubricants were examined. Statistical analysis of the change in NOx conversion revealed that the loss in NOx conversion was proportional to and mainly dependent on the rate of total sulfur exposure, regardless of the sulfur source. In addition, the results of this study allow review of the effects of engine oil sulfur in perspective to the future EPA mandated ultra low sulfur diesel fuel. It should be noted that this work describes only initial sulfur poisoning studies and that no evaluations of NOx adsorber desulfations are addressed.

Coated Valve Train Components and Low Emission Engine Oils in a Fired Engine Enviroment

A series of heavy-duty diesel, fired engine tests were run using coated valve train components in combination with low emission diesel engine crankcase oils. Examination of coated rocker arm and corresponding, uncoated crosshead surfaces, showed that greater crosshead wear was encountered using a physical vapor deposition (PVD) chromium nitride coating, as compared with that observed using a tungsten carbide PVD composition, or an uncoated rocker arm surface. Good coating adhesion was observed with both coatings, with no adverse effects on neighboring, uncoated surfaces. Tungsten carbide in combination with the first of two low-emission engine oils out performed either of the oils used in combination with chromium nitride. Test parameters are summarized along with key engine data obtained. Observations from surface characterization of representative rocker arm and mating crosshead components, using optical and scanning electron microscopy coupled with energy dispersive spectrometry also are highlighted and discussed.Copyright