Thursday, 30 September 2010

Don't run your engine in gear whilst battery charging.

I nipped over to the marina to visit Rosie for the first time in three weeks. First thing I noticed was that the volt meter was on the low side. After faffing about for a while I realised that the shore line circuit breaker had tripped. That had automatically put the fridge on  Rosie onto battery power via the inverter. Unsurprisingly all the food inside had gone off and there was a certain smell. I started up the engine and watched the battery console as the alternators started to blast about 80 amps into the battery pack. Whilst this was happening I checked the land-line to find it had fallen down between the jetty and the gunwale and had chaffed through. so now I knew what had caused the problem. I have a spare cable which was swapped over to restore mains power to the Beta charger.

I have been puzzled for some time about narrow boat engines that are being run by their owners to charge a battery whilst moored and why the engine needs to have the propeller in gear. What I do know is that this will cause some damage to the canal if the boat is moored and the engine is run for long periods in gear. Now I am no wizz kid when it comes to engines, but I can find my way around them if needs be.

I was unsure if this additional load actually needs to be placed on an engine. There is already a load put on the engine by the alternator(s) when charging batteries. So is there a real reason to require an additional load on an internal combustion engine when ticking over or at faster speeds?

There is much "folk law or urban legends" promulgated on the canal forums, so I decided to look into the real effect of such issues. The road transport industry in the UK have had a number of "Anti-idling campaigns" over the last few years. In none of the campaigns has reduced costs in engine maintenance been included or flagged as being a significant cost saving issue.

However, I did find several research papers on the subject. "The effect of load and viscosity on the minimum operating oil film thickness of piston-rings in internal combustion engines"
By S J Söchting and I Sherrington 2009

Abstract: Computer simulations are now routinely used in the design and analysis of ring packs for internal combustion engines. Commonly they predict that an increase in engine load decreases minimum operating film thickness because oil availability and oil transport through the ring pack are reduced under these conditions. To assess the reliability of new simulations, investigators compare the output of computer models with experimental measurements of parameters on operating engines. Contributing to this process this paper presents an experimental study of an investigation into the effect of load on the minimum oil film thickness between piston rings and cylinder liner in a fired compression ignition engine. Oil film thickness data were collected using capacitance-based transducers located near top dead centre and mid-stroke. Experiments were performed at 2000 r/min using two mono-grade oils (SAE 50 and SAE 20) and one multigrade oil (SAE 5W50) under a range of fixed engine loads.

The interesting information is contained in the graphs which highlight the oil thickness at the scraper and compression rings. The load on the engine is varied whilst the engine speed is kept constant. The oil thickness was measured for each stoke of the engine - inlet, compression, ignition and exhaust. What this data actually supports is that modern oil and modern pistons, rings and bore combinations have reduced moving part wear rates significantly.

However, in engines that have experienced significant wear on the pistons, rings and bores. Even where modern oils and engineering technologies to the pistons, rings and bores have been deployed. Increasing the load increases the wear rate.

I found a further research paper "Investigation of fundamental wear mechanisms at the piston ring and cylinder wall interface in internal combustion engines"
By P Papadopoulos, M Priest and W M Rainforth 2007.

Abstract: This research examined the cylinder liner–piston ring system simultaneously from the metallurgical and metrological standpoints, using specimens cut from real engine components (rings and liners), in order to identify the mild and severe wear mechanisms. Work has been conducted using a Plint TE77 high frequency friction machine. Metrological analysis was performed using stylus contacting profilometer. Metallurgical analysis of the samples was carried out using a JOEL JSM-6400 scanning electron microscope. In addition to wear, the coefficient of friction (μ) was recorded for every piston ring – cylinder liner pair so as to observe the transitions between mixed and boundary lubrication. This paper presents the results obtained using flame sprayedMo-coated spheroidal graphite cast iron, which is an old piston ring coating and is not available anymore, and relatively new Federal Mogul CKS-36TM top compression rings tested against a grey cast iron cylinder liner tested at two different bulk oil temperatures (90 ◦C and 140 ◦C), two different pressures (3.9MPa and 6.5MPa) and with two different lubricants (SAE 0W20 with a FrictionModifier and SAE 15W40).

What this data actually supports is that modern oil and modern pistons can be used on old engines to reduce moving part wear rates significantly. In older engines where modern oils, metallurgical and engineering technologies to the pistons, rings and bores have been deployed, load has little effect on increased wear rate.

A further research paper "The effects of soot-contaminated engine oil on wear and friction: a review"
By D A Green and R Lewis 2006

Abstract: During the diesel engine combustion process, soot particles are produced and are either exhausted into the atmosphere or absorbed by the engine’s lubricant. Soot-contaminated lubricant has been shown to produce significant amounts of engine wear. The main mechanism of soot-related wear is through abrasion, but, at increased levels of soot content in the lubricant, starvation of the contact can occur, which can increase wear further. High concentrations of soot can increase the local acidic level and, around the piston where high temperatures and volatile gases coexist, corrosion may also occur. In this paper, the current understanding of engine wear due to soot contamination and the previous research performed is reviewed. The paper also discusses soot formation and its general effects within the engine (including friction and efficiency), as well as other issues including filtration or removal, effects on the lubricant, engine design and operation, and future industry targets and technologies related to soot contamination.


This review paper has brought together a significant amount of information and research in the field of soot-contaminated lubricants and the associated engine wear problem. It has been shown essentially that, in fuel-rich and high-load engine operating conditions, soot production increases dramatically; the primary soot particles of approximately 40nm diameter are either transported to the exhaust system or absorbed by the lubricant. When absorbed by the lubricant, the soot particles tend to agglomerate into clumps of an approximate mean diameter of 200nm. If EGR (a technique used to reduce NOx emissions) is fitted to the engine, then some of the exhausted air is reintroduced into the engine, increasing the soot loading in the lubricant. Soot-contaminated lubricants have been shown to increase the wear of many engine components. An engine’s valve train has proven to be the most seriously affected because of the thin oil-film thicknesses experienced in many of its reciprocating contacts. The film thicknesses produced in such contacts have been shown to be less than the diameter of the soot particles contained within the lubricant. To understand the degree to which soot in a lubricant increases component wear and, more importantly, the wear mechanisms that cause the wear, various tests have been performed. The tests have included a laboratory bench test all the way through to full engine tests. Each type of test provides more information to add to the increasing knowledge on the subject. The dominant wear mechanism that has been discovered is abrasion, but the more serious starvation wear mechanism, which occurs at very high soot contamination levels, could lead to engine failure as contacts may end up operating unlubricated. Soot contamination has also been shown to affect adversely the properties of lubricants, in particular increasing the viscosity, which in turn increases contact friction, leading to a reduction in engine efficiency. This will increase fuel consumption and, therefore, tailpipe carbon dioxide emissions.

Investigations are required into the actual removal of the particles from the lubricant, to attempt to reduce the potential that wear occurs. A reduction in the amount of soot produced through the combustion process can be achieved through development of current diesel fuels and through the introduction of synthetic diesel fuels where tighter component control is possible owing to the nature of the production process. Biofuels are also showing promise as they naturally tend to produce less combustion soot than current diesel fuels. Finally, improvements in lubricant technology can assist in the retention of soot particles and antiwear performance through additive improvements. Also, increased wear protection can be achieved through the very high viscosity indices possible with modern synthetic lubricants.

So if you need to charge your battery bank, removing the load from the engine, by disengaging the propeller will reduce wear and tear on your engine. Reduced loads mean less soot production and acidic levels in the engine oil. Regular oil and filter changes will also reduce the wear and tear on your engine.


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