Friction-Enhancing Properties of ZDDP An... Reaction Films
Quote:
Abstract: Many phosphorus-base antiwear films, including those formed by zinc dialkyl dithiophosphates (ZDDP), cause significant increase in friction in thin film, high-pressure lubricated contacts. This can have a deleterious effect on engine oil fuel efficiency. Previous work has shown than friction in increased not under boundary, but under mixed lubrication conditions and it has been suggested that this phenomenon results from an effective roughening of the rubbing surfaces by the formation of unevenly-distributed reaction films.
In the current paper it is shown that, when other additives commonly used in engine oils are added to ZDDP solutions, quite smooth ZDDP reaction films can result. Despite this, the ZDDP still produces a marked increase in friction in mixed lubrication conditions, which suggests that surface roughening is not the main origin of friction enhancement by ZDDP reaction films. In a companion paper, Part II, it is shown that ZDDP reaction films, whether rough or smooth, enhance friction by inhibiting the entrainment of liquid lubricant into rubbing contacts, thereby reducing the elastohydrodynamic oil film thickness.
An interesting article pointing out a lesser known property of ZDDP that I think some people may misunderstand. I think a lot of people have the false belief that ZDDP is a friction reducing additive when the opposite is usually true.
It also validates the reductions in ZDDP over the years beyond just for the purpose of not poisoning the catalysts. Since fuel efficiency is not only an environmental concern but a performance concern as well it makes more sense to advance beyond ZDDP focused formulations.
Quote:
Abstract: Many phosphorus-base antiwear films, including those formed by zinc dialkyl dithiophosphates (ZDDP), cause significant increase in friction in thin film, high-pressure lubricated contacts. This can have a deleterious effect on engine oil fuel efficiency. Previous work has shown than friction in increased not under boundary, but under mixed lubrication conditions and it has been suggested that this phenomenon results from an effective roughening of the rubbing surfaces by the formation of unevenly-distributed reaction films.
In the current paper it is shown that, when other additives commonly used in engine oils are added to ZDDP solutions, quite smooth ZDDP reaction films can result. Despite this, the ZDDP still produces a marked increase in friction in mixed lubrication conditions, which suggests that surface roughening is not the main origin of friction enhancement by ZDDP reaction films. In a companion paper, Part II, it is shown that ZDDP reaction films, whether rough or smooth, enhance friction by inhibiting the entrainment of liquid lubricant into rubbing contacts, thereby reducing the elastohydrodynamic oil film thickness.
An interesting article pointing out a lesser known property of ZDDP that I think some people may misunderstand. I think a lot of people have the false belief that ZDDP is a friction reducing additive when the opposite is usually true.
It also validates the reductions in ZDDP over the years beyond just for the purpose of not poisoning the catalysts. Since fuel efficiency is not only an environmental concern but a performance concern as well it makes more sense to advance beyond ZDDP focused formulations.