Traton, Navistar Problem Different Emission Methods

[Find the latest in equipment & maintenance: Explore this quarter’s issue of Calibrate]

Wanting again on writing about truck know-how for a few years, there have been just some standout engine introductions. The introduction of the Cummins Signature 600/ISX, with twin overhead camshafts, was certainly one of them. One other was Caterpillar’s introduction of the ACERT engine. It generated far much less oil soot than others of the time, whereas controlling NOx with out exhaust gasoline recirculation (EGR). It’s nonetheless utilized in marine and building markets.

A 3rd was Detroit Diesel’s D15 with the primary true common-rail injection system. Volvo’s introduction of fuel-efficient turbo-compounding together with their wave piston was a fourth. The latest introduction of the Navistar S13 engine with no EGR cooler and far much less reliance on any type of EGR is a exceptional fifth.

Get away the champagne!

All however eliminating the necessity for EGR within the engine is a giant benefit as a result of it would definitely cut back each gas consumption and the price of repairs. For longer than a decade, all diesel makers have used jacket-cooled EGR to considerably cut back dependence on selective catalytic discount (SCR) and the diesel exhaust fluid (DEF) that allows it to kill NOx. All of them engaged in a cautious balancing act — barely improve engine stress and complexity with the EGR system, however decrease the necessity for DEF and due to this fact its price. Now, Navistar and Traton appear to have thrown out the rulebook with an engine that harks again to the golden days of diesel engineering, when EGR was a management know-how used solely on passenger automobiles. Such issues don’t occur typically.

The secrets and techniques to the S13’s extraordinary capacity to kill NOx relate to 2 elements: First, SCR (just like the diesel particulate filter or DPF), as usually configured, solely actually works at full effectiveness when the engine is beneath load. And, vans sadly have to drive at low speeds, crawl alongside in visitors at occasions, heat up after chilly begins and idle. Getting SCR to work at full effectivity far more of the time is a part of the brand new system’s secret, and that’s purely a matter of temperature.

Navtej Singh, Navistar’s chief engineer for powertrain methods, says, “In an effort to retain warmth and decrease the again stress, the dual-stage aftertreatment system was developed. This method has twin SCR to regulate the NOx emissions and a DPF to regulate the particulate matter [PM] emissions passively.”

Singh defined that the exhaust stream recirculates inside the aftertreatment (one field) system and helps in sustaining the warmth, particularly for low-load cycles, and thus reduces the necessity to set off SCR warmup mode (which additionally helps in gas effectivity enhancements).

“The exhaust gasoline recirculation together with different combustion methods is used to heat up the exhaust aftertreatment quicker and hold it heat throughout difficult working situations, like startup, idling and low-load situations,” he stated.

The opposite trick is getting two cracks on the NOx with two dosers and two SCR reactors, a course of that’s additional enhanced by means of uncooled exhaust to extend the temperature of the 2 SCR catalysts.

On this connection, Singh goes on to say, “This aftertreatment system consists of an SCR to DPF to SCR configuration. The upstream diesel exhaust fluid doser, which is the primary doser, is nearer to the engine turbocharger and will get the benefit of the recent temperature. This helps in decreasing the NOx over the primary SCR catalyst particularly in low-load cycles or startup situations. The downstream DEF doser, which is the second doser, performs a key function in decreasing remaining NOx over the second, predominant SCR catalyst.”

Brian McGreevy, program chief engineer for S13 Built-in Powertrain, summed up the idea: “The design philosophy of the powertrain is to have the NOx emissions discount achieved primarily by means of selective catalytic discount within the aftertreatment. The S13 Built-in Powertrain’s engine doesn’t have an EGR cooler however nonetheless has EGR, which is simply used to maintain the aftertreatment heat for preliminary startup, idling and different low-load situations. With out vital EGR utilization in regular driving situations and never getting used as a major a part of the emissions discount, an EGR cooler just isn’t wanted.

“The twin-stage SCR in a one-box design is a key enabler of this technique. With the removing of the EGR cooler and practically no EGR, the engine generates much less soot and PM, however has a robust NOx management supplied by the dual-stage SCR. Much less soot and PM generated additionally helps extending DPF service intervals. Since there is no such thing as a lively DPF regen, no gas dosing within the aftertreatment system is required.”

The web impact of such a system can be to save lots of gas, probably a substantial quantity through engine effectivity, however at the price of a minimum of some improve in DEF utilization. McGreevy says, “The design intent was to not cut back engine-out NOx however to attain probably the most environment friendly combustion attainable. This was made attainable as a result of effectiveness of the aftertreatment system for NOx conversion.”

Remember that the S13 has a 23:1 compression ratio, an efficiency-improving change that turns into sensible with low-soot combustion, which in flip is a product of EGR-less operation beneath regular masses. It should even have a less complicated turbo that usually would require much less backpressure to function, in addition to barely decrease parasitics resulting from a considerably much less highly effective common-rail injection system, sensible when there is no such thing as a exhaust within the combustion recipe more often than not.

It’s very probably that there might be appreciable financial savings in different prices as effectively to offset the DEF utilization, together with the beforehand talked about discount in DPF cleanings, the elimination of the EGR cooler, and probably nonetheless longer oil change intervals than we see even with different engines in the present day. McGreevy says, “There may be extra info to return concerning improved service and fluid change intervals, in addition to DEF consumption charges. On DEF consumption particularly, we count on all OEMs to have elevated DEF utilization for 2024 GHG-certified powertrains.”

Different OEMs are probably taking a look at comparable EGR-less configurations for 2024. Two that probably gained’t are Volvo and Mack with their turbo-compounding system. Inserting a turbine that captures exhaust vitality and transfers it to the crankshaft after the turbo is a perfect option to make an engine with a jacket water-cooled EGR system extra environment friendly. Variable-geometry turbos, or the asymmetrical design Detroit Diesel makes use of, shift the usual turbo’s excellent stress steadiness in an undesirable route. Typical turbos really assist drive the truck down the street by producing consumption enhance stress ranges which are barely greater than exhaust backpressures. EGR methods want backpressure that’s far sufficient above enhance stress to drive the exhaust by means of the cooler and into the consumption system. Turbo-compounding makes efficient use of this stress in grabbing extra vitality out of the combustion course of slightly than throwing it away. Thus, there will definitely be a horse race between EGR-less engines and engines with turbo-compounding within the gas economic system derby.