Pathway to 50% Brake Thermal Efficiency using Gasoline Direct-Injection Compression-Ignition (GDCI) 2019-01-1154
Continued improvement in the combustion process of internal combustion engines is necessary to reduce fuel consumption, CO2 emissions, and criteria emissions for automotive transportation around the world. One consequence of increased engine efficiency is lower exhaust temperatures. This presents challenges for both turbocharging and aftertreatment.
In this paper, test results for the third generation Gasoline Direct Injection Compression Ignition (GDCI) engine are presented. The engine is a 2.2L, four-cylinder, double-overhead-cam engine with compression ratio ~16:1. A 2.5kW electric air heater positioned upstream of the intake valves is used for cold starts; no spark plugs are used. The engine features a wetless combustion system with a high-pressure GDi fuel system. At low load, exhaust rebreathing was used to promote autoignition and elevate exhaust temperatures to maintain high catalyst conversion efficiency. For higher loads, a new GDCI-diffusion combustion strategy was combined with advanced single-stage turbocharging to produce excellent low-end torque and power. Time-to-torque (TT) simulations indicated 90% load response less than 1.2 seconds without a supercharger.
Dynamometer tests indicated unprecedented levels of fuel efficiency over the operating map. Minimum BSFC of 194 g/kWh (BTE 43%) was measured at 1750rpm with BSFC less than 210 over a very wide operating band. The GDCI engine, which operates on commercial pump gasoline, is ideal for down speeding and uploading for improved vehicle fuel economy.
While actual vehicle tests were not conducted, vehicle simulations were performed for a midsize sedan in the US fleet. Results indicated a 32.8% improvement in combined FTP fuel economy over a competitive 2015 1.6L turbocharged GDi engine equipped with cam phasing and variable valve lift. Further fuel economy benefit is available with start/stop systems and mild hybridization.
Mark Sellnau, Matthew Foster, Wayne Moore, James Sinnamon, Kevin Hoyer, William Klemm