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Figure 42 - Volatile content of oil samples measured by GC, after [4] *TRZ =top ring zone

Figure 42 - Volatile content of oil samples measured by GC, after [4] *TRZ =top ring zone

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The lubricant influences the tribological performance, fuel economy and the emissions of the internal combustion engine. The interaction between the lubricant, the piston ring pack and its environment plays the most significant role in the control of oil consumption, affecting emissions, fuel economy and fuel economy retention through friction, and overall engine performance, such as wear. It is an artefact of the design of the ring pack and the need for there to be some lubrication between rings and liners that a small amount of oil passes the top ring and enters the combustion chamber. This results in oil consumption as it is lost to the exhaust where it adds to the emissions. This consumed oil also reduces the effectiveness of the gasoline after-treatment catalysts by forming a film of phosphorus over the catalytic surface. For this reason oil manufacturers are being legislated to reduce the quantity of sulphur and phosphorus contained in engine oil (from 0.12% in 1994 through 0.10% in 2001 for GF-3 to 0.08% in 2004 for GF-4). Some of the thinnest oil films in an engine are found between the top ring and the liner, at times operating in boundary lubrication conditions, as shown in Figure 1, hence permitting contact between these components, and it is partly for this reason that the piston assembly accounts for 40-60% of total engine friction.
The lubricant influences the tribological performance, fuel economy and the emissions of the internal combustion engine. The interaction between the lubricant, the piston ring pack and its environment plays the most significant role in the control of oil consumption, affecting emissions, fuel economy and fuel economy retention through friction, and overall engine performance, such as wear. It is an artefact of the design of the ring pack and the need for there to be some lubrication between rings and liners that a small amount of oil passes the top ring and enters the combustion chamber. This results in oil consumption as it is lost to the exhaust where it adds to the emissions. This consumed oil also reduces the effectiveness of the gasoline after-treatment catalysts by forming a film of phosphorus over the catalytic surface. For this reason oil manufacturers are being legislated to reduce the quantity of sulphur and phosphorus contained in engine oil (from 0.12% in 1994 through 0.10% in 2001 for GF-3 to 0.08% in 2004 for GF-4). Some of the thinnest oil films in an engine are found between the top ring and the liner, at times operating in boundary lubrication conditions, as shown in Figure 1, hence permitting contact between these components, and it is partly for this reason that the piston assembly accounts for 40-60% of total engine friction.
Figure 3 - TRZ oil carbonyl levels and sump carbony] levels (x100), after [3] Figure 2 - TRZ piston (a) and schematic of engine (b) with sample pipe, after [10]
Figure 3 - TRZ oil carbonyl levels and sump carbony] levels (x100), after [3] Figure 2 - TRZ piston (a) and schematic of engine (b) with sample pipe, after [10]
Additional work into the chemical mechanisms of the degradation of the oil was undertaken at the Chemistry Department, University of York. Readers interested are directed to papers from that institution [3, 7-9]. Some results for carbonyl concentration are presented in Figures 3 and 6, and described in section 2.3.
Additional work into the chemical mechanisms of the degradation of the oil was undertaken at the Chemistry Department, University of York. Readers interested are directed to papers from that institution [3, 7-9]. Some results for carbonyl concentration are presented in Figures 3 and 6, and described in section 2.3.
elements. It is possible for these volatiles to enter the gas state and be drawn into the exhaust gas, having a detrimental effect upon emissions. With consideration to future problems posed to lubricant formulation, initial work has suggested that bio-fuels are likely to have increased absorption levels into the TRZ oil and, ultimately, the sump. This will change the sump oil formulation from the optimum designed and may effect the frictional characteristics of the oil throughout the engine resulting in reduced fuel economy.
elements. It is possible for these volatiles to enter the gas state and be drawn into the exhaust gas, having a detrimental effect upon emissions. With consideration to future problems posed to lubricant formulation, initial work has suggested that bio-fuels are likely to have increased absorption levels into the TRZ oil and, ultimately, the sump. This will change the sump oil formulation from the optimum designed and may effect the frictional characteristics of the oil throughout the engine resulting in reduced fuel economy.
Figure 5 shows the friction results obtained from this extracted oil when tested in a Plint TE-77 reciprocating tribometer. The test parameters were set to simulate the ring and liner contact conditions in the most severe conditions just after combustion and the material used was that of the engine liner for both the pin and the plate. It is clear from the figure that there are distinct differences between all the samples, but most notably between the sump oil and fresh oil samples and the four top ring zone samples which is the oil that lubricates the ring/liner interface.
Figure 5 shows the friction results obtained from this extracted oil when tested in a Plint TE-77 reciprocating tribometer. The test parameters were set to simulate the ring and liner contact conditions in the most severe conditions just after combustion and the material used was that of the engine liner for both the pin and the plate. It is clear from the figure that there are distinct differences between all the samples, but most notably between the sump oil and fresh oil samples and the four top ring zone samples which is the oil that lubricates the ring/liner interface.
By taking both TRZ samples and sump samples, and measuring the carbony] concentration of both sets of samples it is possible to calculate the flow rates of degraded oil from the ring pack to the sump. This is because if the sump is maintained at 70°C, a temperature at which negligible degradation occurs, the degradation of the sump oil is caused by the degraded oil returning from the ring pack. This results in a steady increase in degradation in the sump over time. Figure 6 shows the carbony] species in the sump increasing (b) compared to the fairly constant level of degraded sample taken from the ring pack (a) with respect to time. The results presented are for the same speed, 1500 r/min, and three different loads as indicated on the graph. The 50% load experiment was undertaken twice to investigate repeatability. The carbonyl content does not start at zero for the sump oil at the start of the test. This is because, despite flushing the engine, residual carbonyl from previous tests was present in the sump oil.
By taking both TRZ samples and sump samples, and measuring the carbony] concentration of both sets of samples it is possible to calculate the flow rates of degraded oil from the ring pack to the sump. This is because if the sump is maintained at 70°C, a temperature at which negligible degradation occurs, the degradation of the sump oil is caused by the degraded oil returning from the ring pack. This results in a steady increase in degradation in the sump over time. Figure 6 shows the carbony] species in the sump increasing (b) compared to the fairly constant level of degraded sample taken from the ring pack (a) with respect to time. The results presented are for the same speed, 1500 r/min, and three different loads as indicated on the graph. The 50% load experiment was undertaken twice to investigate repeatability. The carbonyl content does not start at zero for the sump oil at the start of the test. This is because, despite flushing the engine, residual carbonyl from previous tests was present in the sump oil.
Initial research [12], Figure 8, suggests that a higher viscosity lubricant will flow through the ring pack more slowly than a lower viscosity lubricant. Therefore as lubricants degrade and hence become more viscous they may remain in the ring pack, exposed to the degradation process, for longer. Although the speed at which the oil in the ring pack degrades will remain the same it will become highly degraded due to being present for longer and so it is likely to result in higher levels of sludge, varnish and then deposit formation before the lubricant is due to flow back to the sump. This will have additional detrimental effects on fuel economy over and above the increased viscosity of the lubricant as well as affecting the action of the rings and hence ultimately affecting emissions as they will no longer seal against the bore correctly.
Initial research [12], Figure 8, suggests that a higher viscosity lubricant will flow through the ring pack more slowly than a lower viscosity lubricant. Therefore as lubricants degrade and hence become more viscous they may remain in the ring pack, exposed to the degradation process, for longer. Although the speed at which the oil in the ring pack degrades will remain the same it will become highly degraded due to being present for longer and so it is likely to result in higher levels of sludge, varnish and then deposit formation before the lubricant is due to flow back to the sump. This will have additional detrimental effects on fuel economy over and above the increased viscosity of the lubricant as well as affecting the action of the rings and hence ultimately affecting emissions as they will no longer seal against the bore correctly.
Table 2 - Residence times in the Piston Assembly with respect to engine speed and load, after [12]
Table 2 - Residence times in the Piston Assembly with respect to engine speed and load, after [12]
Figure 9 - Comparison of piston assembly friction power loss for SAE OW 20 without FM (friction modifier) and SAE 5W30 with FM lubricants, after [14] The vast majority of the frictional losses in an engine are attributable to the three main tribological sub- systems of an engine; the piston assembly, engine crankshaft bearings and the valve train. Experimental methods have been developed for the Hydra engine at Leeds that allow the losses in all three tribological components to be measured while the engine is fired. This involves the use of specially designed torque transducers on the drive pulleys of the valve train, the indicated mean effective pressure technique to obtain the piston assembly friction and the calculation of crankshaft bearing losses by subtraction. This method has confirmed that between 40 and 60% of the total engine friction is due to the piston assembly and has shown the effect of speed and lubricant viscosity on power-loss in the piston assembly, Figure 9. This work has been reported by Mufti et al [13, 14].
Figure 9 - Comparison of piston assembly friction power loss for SAE OW 20 without FM (friction modifier) and SAE 5W30 with FM lubricants, after [14] The vast majority of the frictional losses in an engine are attributable to the three main tribological sub- systems of an engine; the piston assembly, engine crankshaft bearings and the valve train. Experimental methods have been developed for the Hydra engine at Leeds that allow the losses in all three tribological components to be measured while the engine is fired. This involves the use of specially designed torque transducers on the drive pulleys of the valve train, the indicated mean effective pressure technique to obtain the piston assembly friction and the calculation of crankshaft bearing losses by subtraction. This method has confirmed that between 40 and 60% of the total engine friction is due to the piston assembly and has shown the effect of speed and lubricant viscosity on power-loss in the piston assembly, Figure 9. This work has been reported by Mufti et al [13, 14].
Figure 10 - TE77 piston assembly friction coefficients for non additivised oil and three different additivised oils.
Figure 10 - TE77 piston assembly friction coefficients for non additivised oil and three different additivised oils.
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