Bosch’s Wild New Way to Clean Up Gas Engines Starts With a Flame

It seems weird to learn about breaking “emissions control news,” even as the present administration rolls back emissions regulations, but remember that most such rollbacks have affected CO2 emissions. The so-called “criteria emissions”—ozone, particulate matter, carbon monoxide, lead, sulfur dioxide, and nitrogen dioxide—are still recognized as hazardous to public health and the environment, so they’re still fully regulated. This new Bosch Rapid Catalyst Heater promises to help make all gas-powered cars run a little cleaner and possibly make plug-in hybrids (PHEVs) run a lot cleaner.

It’s All About Cold Starts

Modern three-way catalytic converters remove up to 98 percent of a gas engine’s criteria emissions after they fully warm up (750–1,100 degrees F). So getting a vehicle to pass the EPA’s emissions test requires a laser focus on the first 20–60 seconds of the 31-minute dynamometer test. The knobs engineers can turn in order to quickly heat a catalyst include (listed in order from cheapest to most expensive): moving the catalyst as close as possible to the cylinders, running a rich fuel mixture at startup, retarding ignition timing, retarding exhaust-cam timing, adding secondary air injection, and using electricity to directly heat the catalyst.

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Components comprising Bosch RCH.

Bosch’s New Knob

Direct electric catalyst heaters have historically added 1–10 kW of electricity to the catalyst “brick,” with 5 kW being most typical—that’s about what the starter draws for a big high-compression engine, so it’s pretty tough to accomplish on a 12-volt system without a hybrid battery onboard. Bosch is promoting a gas burner capable of almost instantly delivering 25 kW of heating energy directly into the exhaust stream immediately ahead of the catalyst.

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List of benefits of Bosch RCH

How it Works

Press the engine-start button, and a burner-control unit starts a typical secondary air-injection type pump drawing filtered air in through a Bosch mass airflow sensor. This air enters the combustion module flowing at roughly 15 cubic feet per minute, where low-pressure fuel is fed to a standard Bosch port injector (with a unique nozzle hole pattern). This fuel is ignited by a Bosch diesel glow plug, and the mixture flows past a Bosch oxygen sensor (targeting a stoichiometric 14.7:1 air-fuel ratio) and flows into the exhaust right at the entrance to the catalyst.

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Air, fuel, and exhaust flow through Bosch RCH

50–65 Percent Reduced HC Emissions

In Bosch testing, delaying engine start to give the RCH a 10-second head start (similar to the wait for a glow plug), the total cycle hydrocarbon emissions (the chief precursor to ozone) were reduced by 50 percent on a full-size SUV and by 65 percent on a light-duty pickup (probably the Ram Hurricane we witnessed the system operating on). Test-to-test variability also drops dramatically.

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Hydrocarbon cold-start emissions, with and without Bosch RCH

What About Frequent PHEV Restarts?

The official FTP 75 test starts with 20 seconds of idling—a condition where 5 kW of direct all-over catalyst-brick heating might compete pretty well with 25 kW of heat being blown in from the front when all the engine catalyst-warming knobs are cranked into position. But say you’re rolling around town in your 5,600-pound BMW X5 xDrive50e PHEV and suddenly need to pull out onto a busy street. That 194-hp electric motor needs help, so the cold engine fires—not at idle with retarded timing, rich fuel, and cat-warming cam phasing, but with a high-power request. In this situation, the Bosch setup will result in cleaner emissions sooner than a 5-kW electric heater could produce if initiated by the same surprise throttle input.

What About Fuel Consumption?

It certainly isn’t nothing, but Bosch claims that cycle emissions should be neutral or lower in the delayed start/RCH-head-start use case (which also applies to any navigation-based predictive engine-start algorithm that might be applied to a PHEV). Note that U.S. particulate emissions don’t typically require a gasoline particle filter catalyst, as European and Chinese regs do, but they may by the end of the decade. If/when they do, the RCH can purge this filter much more efficiently than engine-enrichment strategies alone can.

What About Cost?

Suppliers seldom share specific pricing, but we’re assured that this “knob” is highly competitive with other equally effective technological upgrades. These include: Reinforcing an electrical system to withstand adding a 5-kW electric catalyst heater to a non-hybrid without 48-volt power onboard (this is a 12-volt system), increasing precious-metal loading in the catalyst, and radically redesigning a powertrain.

The system is ready for integration into a manufacturer program, so expect to see it on the road in three to five years.