Cutting emissions with Jacobs CDA
Robb Janak, director of new technology at Jacobs Vehicle Systems, says the company’s cylinder deactivation solution is a win for fuel saving and emissions reduction
Forthcoming tighter emissions regulations in Europe and North America place focus on two crucial areas: particulates from non-exhaust sources, and nitrogen oxides (NOx) emissions from engines operating at sub-optimum loads and temperatures.
Technology from Jacobs Vehicle Systems has a crucial role to play in both these areas, and, unlike many other emissions control systems, could actually reduce vehicle operating costs for operators.
Using engine brakes, such as the famous Jake Brake, takes much of the braking load off the vehicle’s friction brakes and will reduce or eliminate the output of toxic particles from discs and pads.
These particles can penetrate deep into the lungs, causing respiratory diseases, cancers, and an increased risk of Alzheimer’s disease. Using a Jake Brake can generate in the region of 360 kW of braking force from a 13-litre engine irrespective of road speed or operating temperatures, reducing braking particle output in all operations and extending the replacement cycle for wearing brake parts.
Jacobs Vehicle Systems is also using Jake Brake technology to reduce NOx emissions from diesel engines that are idling or operating in low-load conditions.
NOx emissions are symptomatic of high combustion temperatures and pressures, and regulators and vehicle manufacturers therefore initially concentrated on controlling NOx in these conditions.
Their method of choice was Selective Catalytic Reduction (SCR), introducing AdBlue into the exhaust system, where a combination of high exhaust gas temperatures and precious-metal catalysts allowed it to break NOx down and turn it into CO2 and water vapour.
This technology has proved very effective but acceptable NOx limits have fallen drastically since its introduction, increasing focus on the emissions produced by cold-start, idling and low-load conditions.
The problem is that when the aftertreatment system temperature drops below 250°C, NOx conversion by SCR becomes less effective. In prolonged low-temperature conditions, the AdBlue can even crystalise in the dosing unit causing the engine power to de-rate.
Heavy-duty diesel engines typically have unthrottled forced-air induction and in low-load conditions large quantities of air get pumped through the engine, reducing exhaust and aftertreatment system temperatures. These low temperatures can also prevent the passive regeneration of the particulate filter, leading to clogging. This is a well-documented problem on all sizes of diesel engines in urban operations.
Existing solutions typically involve burning extra diesel, which is ultimately unproductive in overall emissions terms, either via an additional injector in the exhaust system or using the multipulse facility in modern electronically-controlled diesel injectors to introduce an extra injection of fuel at the end of the combustion event. These solutions are both wasteful and needlessly complex.
Jacobs’ Cylinder Deactivation (CDA) technical solution is to tackle the problem at the source: raising exhaust temperatures and reducing airflow through the engine in idling and part-load conditions.
In operation, the system, based on existing Jake Brake technology, ensures that valves in selected cylinders are not opened at any time in the four-stroke cycle. The air within is retained as an air-spring. Simultaneously, the fuel injectors are disabled on the selected cylinders.
The result is the remaining active cylinders work harder, burning more fuel while less air in total passes through the engine. Exhaust gas temperature increases in the order of 100 to 200°C are achieved, and the efficiency not only of the SCR system but also the diesel particulate filter is retained. The system can also be actuated on cold starts, forcing the exhaust system temperature up to an acceptable level almost straight away.
There is a further benefit. With half its cylinders disabled, a typical six-cylinder heavy-duty diesel may burn 20 per cent less fuel.
There are obvious advantages for the Jacobs CDA in applications such as city buses which have duty cycles dominated by low-load and idling situations, but beyond that it may lead to greater efficiencies in haulage, too.
For instance, a powerful tipper truck may need every one of its 500 bhp to propel its 32-tonne laden weight up the steep haul road out of a quarry, but for the empty return trip 250 bhp would be more than adequate, and a lot less wasteful.
Previously reported tests in North America revealed CDA reducing NOx emissions from an SCR-equipped Class 8 truck by 77 per cent in part-load conditions, while reducing CO2 output by 12 per cent.
Jacobs CDA technology has been recognised by California Air Resources Board (CARB) and the US Environmental Protection Agency (EPA) as a technology capable of meeting 2024 and 2027 emission targets for low-load drive cycles in combination with an advanced SCR system, and the European and other markets are expected to follow suit as Euro VII/7 and its equivalents are introduced, simultaneous with VECTO standards measuring fuel-efficiency.
Fine-tuning the operation of the Jacobs CDA will enable truck manufacturers to meet different market-specific emissions requirements using the same ‘global platform’ core engines.
It’s not often that improved emissions-control technology offers vehicle users a win-win in terms of increased up-time and reduced fuel consumption too, but the Jacobs CDA has the potential to do just that.
