Impending emissions legislation in North America (EPA 27) and Europe (Euro 7), which covers both NOx and CO2 emissions, are pushing engine designers harder than ever before in the search for greater efficiencies, according to Robb Janak, director of new technology at Cummins Valvetrain Technologies.
Janak tells Transport Engineer that he believes the company‘s Cylinder De-Activation (CDA) “represents a breakthrough” because it enables both lower emissions and improved fuel economy to be achieved, as alternative technologies for lowering emissions by raising aftertreatment temperatures have typically caused fuel consumption to worsen.
The CDA system uses Cummins’ expertise in valve control to automatically shut down selected cylinders in low engine load conditions by leaving their inlet and exhaust valves closed throughout the four-stroke cycle, while the fuel injectors are deactivated.
Janak explains: “The remaining cylinders pick up the load and run more efficiently and hotter, adding a higher temperature, lower flow of combustion air to the aftertreatment. This reduces fuel consumption.
“When additional engine braking is required, the same components that deactivate the cylinders are repurposed to provide vehicle retardation using the latest 1.5-stroke High Power Density version of the Jake Brake compression release engine brake.
“Toxic emissions are also reduced because CDA optimises the efficiency of exhaust aftertreatment systems through thermal management as CDA increases exhaust temperatures at part loads. It also eliminates cooling during engine motoring, where tests also revealed a reduction in parasitic drag when the engine is in over-run, saving fuel.”
According to a recent SAE J1321 (Society of Automotive Engineers) standardised fuel consumption testing of Jacobs CDA, fuel savings of 2.76% were returned, using fully loaded comparison trucks on a highway route in North America over several months of standardised testing. Similar tests on a distribution route returned fuel savings of 2%.
Janak says that every Jacobs valvetrain technology is designed and developed with the same durability and reliability goals and methods used to develop its engine brakes. “We believe our Variable Valve Actuation (VVA) and Cylinder De-Activation (CDA) systems will support our collective sustainable goals while maintaining the vehicle performance our customers expect,” he adds.
In addition to CDA, the company’s 2-Step Variable Valve Actuation systems also can improve emissions and engine efficiency. Early Exhaust Valve Opening (EEVO) provides an in-engine technology to rapidly warm up the aftertreatment, instead of using external systems that are add-on units that can be difficult to package. EEVO uses combustion gases to directly provide the heat needed for aftertreatments to work.
Janak says: “Early or late intake valve closing allows the optimisation of the engine breathing for two modes of operation, such as peak load and low loads, improving the overall efficiency of the engine. When combined with an increased geometric compression ratio, this Miller cycle can achieve even greater engine efficiencies.”
Internal combustion engines (ICE) will be around for a few more decades at least, Janak notes, and as heavy-duty diesel engines have lasted 20-plus years, he asserts that it is critical they are made as efficient and clean as possible.
Janak adds: “Innovations in modifying valve motion can improve the efficiencies of the existing diesel engine. Alternative fuels such as natural gas and hydrogen can use the existing combustion engine as a base and a flexible valvetrain can support optimising combustion on these spark-ignited fuels.”
