Impact of Engine Oil Detergent on Low Speed Pre-Ignition (LSPI) and Fuel Economy Performance 2020-01-1424
Low Speed Pre-Ignition (LSPI), also referred to as Stochastic Pre-Ignition (SPI), Superknock or Megaknock is an undesirable combustion phenomenon that limits the fuel economy, drivability, emissions and durability performance of modern turbocharged gasoline engines. Numerous studies have previously reported that the frequency of LSPI is sensitive to engine oil composition. One of these drivers is the concentration of Calcium, which is usually delivered in the form of a detergent in the additive package. Switching to completely all-Magnesium detergent and/or severely limiting the concentration of Ca in the engine oil have recently been proposed as potential means to reduce LSPI.
In this work, we evaluate the impact of detergent type on LSPI performance as well as on other performance that the modern engine oil needs to deliver. Particularly the impact of detergent type on Fuel Economy performance is evaluated. To ensure a rigorous and high precision measurement of the impact of engine oil on fuel economy, representative of real-world conditions, under well-controlled conditions, the ASTM D8114 test cycle (Sequence VIE) was used to quantify fuel economy performance of the oils. This test utilizes a 3.6L LY7 GM engine installed on a dynamometer test stand, and Brake-Specific Fuel Consumption (BSFC) is measured at 6 different stages, representing different regions on the engine map relevant to real-world operation, and a weighted fuel economy performance is then calculated. For oils with the same formulation style, with all components and concentrations apart from the detergent held constant, the formulation with an all Magnesium detergent had a substantially lower fuel economy performance than the formulation with an all Calcium detergent. This suggests that though a switch to an all-Magnesium formulation, or severely limiting the concentration of Calcium in the engine oil may help reduce LSPI in the relatively small fraction of vehicles in the car park susceptible to LSPI, the perceived benefits may be outweighed by the significant penalty on fuel economy incurred by all the vehicles in the car parc.