The influence of the diesel particulate filter additives (DPA) SATACEN and EOLYS on biodiesel fuel quality has been evaluated. Both additives significantly affected the oxidation stability of neat biodiesel. The influence on acid values and CFPP was found to be only small. Combination of diesel additives with biodiesel additives like oxidation stability and CFPP improvers led to similar results. Results indicated that DPA also lowered the efficiency of the oxidation stability improver Baynox. Furthermore, the CFPP additives Chimec and Infineum were also prone to have a small influence on biodiesel oxidation stability.
Engine Performance Additives
This class of additives can improve engine performance. The effects of different members of the class are seen in different time frames. Any benefit provided by a cetane number improver is immediate, whereas that provided by detergent additives or lubricity additives is typically seen over the long term, often measured in tens of thousands of miles.
Cetane Number Improvers (Diesel Ignition Improvers) Cetane number improvers can reduce combustion noise and smoke. The magnitude of the benefit varies among engine designs and operating modes, ranging from no effect to readily perceptible improvement.
2-Ethylhexyl nitrate (EHN) is the most widely used cetane number improver. It is sometimes also called octyl nitrate. EHN is thermally unstable and decomposes rapidly at the high temperatures in the combustion chamber. The products of decomposition help initiate fuel combustion and, thus, shorten the ignition delay period from that of the fuel without the additive.
The increase in cetane number from a given concentration of EHN varies from one fuel to another. It is greater for a fuel whose natural cetane number is already relatively high. The incremental increase gets smaller as more EHN is added, so there is little benefit to exceeding a certain concentration. EHN typically is used in the concentration range of 0.05% mass to 0.4% mass and may yield a 3 to 8 cetane number benefit.
Other alkyl nitrates, as well as ether nitrates and some nitroso compounds, also have been found to be effective cetane number improvers, but they are not currently used commercially. Di-tertiary butyl peroxide was recently introduced as a commercial cetane number improver.
A disadvantage of EHN is that it decreases the thermal stability of some fuels. The effect of the other cetane number improvers on thermal stability is unknown, but it seems likely that they will be similarly disadvantaged. Several laboratories are investigating this issue.
Injector Cleanliness Additives Fuel and/or crankcase lubricant can form deposits in the nozzle area of injectors â€œ the area exposed to high cylinder temperatures. The extent of deposit formation varies with engine design, fuel composition, lubricant composition, and operating conditions. Excessive deposits may upset the injector spray pattern (see Figure 7-1) which, in turn, may hinder the fuel-air mixing process. In some engines, this may result in decreased fuel economy and increased emissions.
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