Systems Approach to the Improvement of Engine Warm-Up Behaviour

Abstract

Modifications to the coolant and oil circuits of a modern production 2.4L diesel engine have been made in an attempt to promote oil warm up to reduce fuel consumption. The new system used oil to cool EGR gases and incorporates a number of coolant flow control valves to reduce heat loss during warm up. The engine was run over cold start NEDC cycles with various flow strategies as a screening exercise to understand the behaviour of the system. Fuel consumption benefits of up to 4% were observed, but these were accompanied with 3% increases in NO x emissions. Detailed analysis of the coolant flows and temperatures showed that when throttling the flow, the mass of coolant in the degas bottle and radiator could be isolated from the system during warm up, essentially reducing the thermal inertia. Heat transfer directly to the oil from EGR gases rather than via the coolant allowed more heat to be put into the oil, with engine oil supply temperatures up to 6 o C hotter, however it was not possible to verify that the oil was hotter at the bearings, valve train and cylinder liner. The engine strategy was seen to react to the faster warm up and retard injection timing, reducing NOx but also compromising overall fuel consumption benefits. Further tests were conducted with varying injection timing to establish a NOx/fuel consumption trade off to demonstrate further benefits when the engine strategy is included in the operation of novel thermal management systems.

Dynamic modelling of diesel engine emissions using the parametric Volterra series

“…Subsequently, during combustion, more heat is lost to the walls, meaning that combustion occurs at colder temperatures, which makes conditions less favourable for NO x formation. 18,19 CO 2 results from the complete combustion of fuel with atmospheric oxygen; reductions in fuel consumption will lead to reductions in the CO 2 emissions. Consequently, the CO 2 emissions are linked to the efficiency of torque production and therefore to the phasing of combustion with cylinder volume changes as well as parasitic losses (friction losses and accessory systems).…”

Systems optimisation of an active thermal management system during engine warm-up

“…Thermostat opening was also delayed, thus suppressing some radiator losses. 10 The other three active devices were intended to be used to direct heat flow between the coolant and the oil.…”

“…6 Careful placing of coolant control valves can improve the engine behaviour during warm-up by isolating parts of the circuit and effectively reducing the thermal inertia during warm-up. 10 Recent production engines on higher-end applications have employed these systems in the form of switchable coolant pumps, 11 or through the active control of coolant flows. 12 The active systems allow the control of heat flows to the different fluids with some examples encouraging heat flow to engine oil to try to reduce the frictional losses due to oil viscometrics.…”

“…These interactions have been seen to compromise overall FC benefits from improved TMSs and some aspects of the strategy should be included in the active TMS calibration. 10,15 The aim of this work is to establish an optimised calibration for the use of an active TMS that introduces a number of degrees of freedom to the engine. Based on scoping exercises, the injection timing should also be included in the calibration routine.…”

“…Based on scoping exercises, the injection timing should also be included in the calibration routine. 10 …”