During the cold start conditions engine must overcome higher friction loss, at the cost of fuel penalty till the optimum temperatures are reached in coolant and lubrication circuits. The lower thermal capacity of the lubrication oil (with respect to the coolant) inverses the relation of viscosity with temperature, improves engine thermal efficiency benefit. Engine oil takes full NEDC test cycle duration to reach 90°C. This leads to higher friction loss throughout the test cycle, contributing a significant increase in fuel consumption. Increasing oil temperature reduces viscosity, thereby reducing the engine friction. This helps to identify the focus for thermal management in the direction of speeding up the temperature rise during a cold engine starting.
This work aims at the study and experiment of an exhaust recovery mechanism to improve the NEDC fuel economy. The objective of the work is to use the exhaust gas energy, post after treatment system to heat up the engine oil temperature. The work was carried in 3 stages, In the first stage, 1D system level simulation was performed to identify the suitable diameter and location to tap the exhaust gas from the main line. In the second stage, 3D CFD transient flow and heat transfer simulations were performed to optimize the flow and to design the heat exchanger for enhanced heat transfer. In the third stage, the concept is experimentally validated for waste heat recovery and the resultant fuel economy benefits that could be achieved with the current solution.
This paper provides a novel simulation-based approach using a 1D & 3D CFD commercial code to calculate the fuel economy benefits. The optimal heat exchanger and flow path design provides us with an 4% improvement in fuel economy.