Michael L. McMillan

Fuel Effects on Combustion and Emissions in a Direct Injection Diesel Engine

The emissions and performance of five diesel fuels, covering a range of cetane numbers and volatilities, were evaluated at three speeds and equivalence ratios in a single-cylinder, DI diesel engine. Graphical comparisons and regression analysis of the data revealed that cetane number and to a lesser extent volatility are the fuel parameters that most strongly influence emissions and performance, with higher cetane number and higher volatility fuels providing the best performance and lowest emissions.

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.

How Much ZDP is Enough

Zinc dithiophosphate, or ZDP, for over 60 years has been used as an additive in engine oils to provide wear protection and oxidation stability in an efficient and cost effective manner. Unfortunately, ZDP contains phosphorus, and phosphorus is a widely known and accepted poison of automotive catalysts and other emissions system components. Because of this, phosphorus (and ZDP) levels in automotive engine oils have been gradually reduced by about 35% over the last 10-15 years, and further reductions are likely in the future. This paper traces the history of ZDP use in automotive engine oils, and addresses the issue of how much (if any) ZDP is actually required to provide wear protection in todays, as well as yesterdays, engines. The focus in the paper is on wear (including scuffing) protection, and not on the other aspects of ZDP performance, such as providing oxidation stability of the oil. It is assumed that these other functions of ZDP can be provided by other ashless and phosphorus-free additives which do not negatively affect emissions system performance.