No, we’re not talking about football, we’re talking about emissions testing! After testing their vehicle at U.S. Environmental Protection Agency’s (EPA) National Vehicle and Fuel Emissions Laboratory during the Spring Workshop, The Ohio State EcoCAR team returned home with a benchmark status of how their vehicle was performing – and more work to do.
The Ohio State vehicle’s exhaust after treatment system features an electrically-heated catalyst with secondary air injection to enable the vehicle to pre-heat the catalytic converter before starting up the engine. This is beneficial for reducing cold start emissions. About 60-80% of vehicle emissions occur right after engine start-up before the catalytic converter is warmed up to its operating temperature. Pre-heating the catalytic converter eliminates the majority of these emissions. The OSU team was able to do a cold start test with and without the electrically-heated catalyst and found that the pre-heat strategy significantly improved their cold start emissions.
However, during emissions testing, data was showing unexpected oscillations in the vehicle’s exhaust gas flow rate. Upon further investigation, the team found that these dynamics were caused by the check valve between the engine exhaust manifold and the secondary air injection system. The valve is used to seal off the secondary air injection system from the rest of the exhaust system at all times except the pre-heat phase. There are two purposes for doing this: so that when the engine is running, no exhaust gas is able to backflow and damage the air injection pump, and also to prevent unexpected air to flow into the exhaust system, messing up the engine’s precisely-tuned air/fuel ratio control.
Through testing at EPA, The Ohio State team was able to identify this issue and replaced the passive check valve with an electrically-actuated valve that can be controlled on-demand by the engine controller. The team is now fine-tuning its vehicle in preparation for the competition Finals in June!