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A New Method to Warm Up Lubricating Oil to Improve the Fuel Efficiency During Cold Start
Abstract:
Cold start driving cycles exhibit an increase in friction losses
due to the low temperatures of metal and media compared to normal
operating engine conditions. These friction losses are responsible
for up to 10% penalty in fuel economy over the official drive
cycles like the New European Drive Cycle (NEDC), where the
temperature of the oil even at the end of the 1180 s of the drive
cycle is below the fully warmed up values of between 100°C and
120°C. At engine oil temperatures below 100°C the water from the
blowby condensates and dilutes the engine oil in the oil pan which
negatively affects engine wear. Therefore engine oil temperatures
above 100°C are desirable to minimize engine wear through blowby
condensate. The paper presents a new technique to warm up the
engine oil that significantly reduces the friction losses and
therefore also reduces the fuel economy penalty during a 22°C cold
start NEDC. Chassis dynamometer experiments demonstrated fuel
economy improvements of over 7% as well as significant emission
reductions by rapidly increasing the oil temperature. Oil
temperatures were increased by up to 60°C during certain parts of
the NEDC.
It is shown how a very simple sensitivity analysis can be used
to assess the relative size or efficiency of different heat
transfer passes and the resulting fuel economy improvement
potential of different heat recovery systems system. Due to its
simplicity the method is very fast to use and therefore also very
cost effective. The method demonstrated a very good correlation for
the fuel consumption within ±1% compared to measurements on a
vehicle chassis roll.