Jacobs CDA technology returns 2.76% fuel saving in highway tests
16 July 2024
Cummins Valvetrain Technologies announced positive results from on-road testing of its Jacobs® cylinder deactivation (CDA) technology for heavy-duty vehicles.
Fuel savings of 2.76% were returned in the first SAE J1321 standardized fuel consumption testing of Jacobs CDA, using fully loaded comparison trucks on a highway route in North America. Similar tests on a distribution route returned fuel savings of 2%.
Impending NOx and CO2 emission legislation in the USA and Europe is pushing engine designers harder than ever before in the search for greater efficiencies, Cummins said. Working from a 2019 baseline, the EU will require a 45% reduction in CO2 by 2030, a 65% reduction by 2035, and a 90% reduction by 2040.
The CDA system uses Jacobs’ 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 their fuel injectors are deactivated. 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.
Criteria pollutant emissions are also reduced because CDA increases exhaust temperatures at part loads, which increases the efficiency of emission aftertreatment systems. CDA also eliminates cooling during engine motoring, where Cummins’ tests also revealed a reduction in parasitic drag when the engine is in over-run, saving fuel.
The tests were conducted using a 2018 International LT625 6×4 tractor unit with a 13 L Navistar A26 450 hp diesel engine and Eaton Endurant 12-speed overdrive AMT gearbox, with a gross vehicle weight of 66,000 lbs. Tests were conducted over 12,000 miles in Q4 2023. The truck was run multiple times both with and without CDA active via a dashboard switch. The truck recorded an average speed of 51 mph on the highway route, and 38 mph on the distribution route.
Every run saw the test truck accompanied by a comparable control vehicle with its fuel consumption also recorded, to provide a baseline to account for variations caused by external factors such as weather and traffic conditions.
The on-road, real-world results from a fully loaded truck follow the reporting by Jacobs of initial fuel economy improvements of up to 20% in dynamometer-based lab testing of an engine in idle mode in 2020. In that same lab test, 77% reduction in NOx was recorded on a low load cycle with a 2018 aftertreatment system. While NOx emission testing was not a focus for the latest test, Cummins expects further improvements in NOx performance due to the benefits of CDA thermal management.
CDA reduces the number of active cylinders to match the driver's real-time torque demand. The active cylinders have higher loads and temperatures, while the inactive cylinders have reduced parasitic losses. The reduced airflow, and air-fuel ratio in the remaining active cylinders, help maintain exhaust system temperatures above the critical 250°C mark to allow efficient NOx conversion by the SCR module and continued passive regeneration of the diesel particulate filter.
On the highway tests without CDA, temperatures in the truck’s SCR unit fell below 250°C for over 15% of the journey time, but when CDA was used in concert with the Jacobs Engine Brake, SCR temperatures fell below 250°C only during the scheduled stops and trailer swaps. On the distribution route, the mean temperature of the SCR unit was 243°C with CDA engaged; 16% above the figure recorded without cylinder deactivation.
Time spent with the SCR operating under 250°C was reduced by over 21%, and SCR temperature with CDA only fell below 200°C for under two percent of the time compared to over 10% of the time in 6-cylinder mode.
The on-road testing also showed that, with optimized engine and cab mounts, NVH was equivalent to the non-CDA-equipped standard engine and vehicle while at 600 rpm in idle, as measured at the driver’s seat.
Source: Cummins