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New EGR Cooler with Bypass Reduces Incomplete Combustion

A conventional EGR Cooling System.

Nikkei. Tokyo Radiator Mfg. Co., an established maker of cooling systems, has developed a new exhaust gas recirculation (EGR) cooler with a bypass channel to reduce incomplete combustion and the resulting emissions of hydrocarbons and soot.

NOx forms primarily due to the presence of oxygen and high temperatures. By recirculating exhaust gas back into the cylinders, EGR lowers the heat of combustion and thereby reduces NOx. EGR coolers further lower the temperature of the exhaust gas before recirculation, thereby achieving an even greater reduction in NOx.

However, the constant use of cooled exhaust gas results in the engine taking longer to reach optimal combustion temperatures. Incomplete combustion—and the associated emissions—can result during that period.

Tokyo Radiator’s new EGR cooler has a built-in bypass channel to send exhaust gases directly back to the combustion chambers when the engine temperature is low. Sensors calculate the engine temperature from the temperature of the radiator coolant, and a pressure valve opens the bypass channel whenever the temperature is below a set value. This helps the engine warm faster, reducing the time for incomplete combustion.

The company plans to mass-produce the new EGR cooler starting this fall. GM reportedly plans to use the device in passenger cars for Europe next year.

Schematic of advanced EGR system for the Ricardo-GM ADEC engine. Click to enlarge.

GM and Ricardo have been developing an advanced diesel engine control (ADEC) system designed to enable consistent achievement of very low emissions levels through closed loop control of the combustion process. An EGR Cooler with bypass is part of that development, which the partners will demonstrate on a 1.9-liter engine.

The ADEC coordinator uses a range of sensors to measure combustion states and then establishes the optimal balance of fuel quantity and timing and air path control (the latter being where the EGR cooler with bypass system comes in).



Sid Hoffman

That's a pretty slick system. It appears they show a turbocharger in both pictures, so I assume it's designed mainly just for diesel engines, not gasoline, although I suppose it could work on either. It looks from the first diagram that they propose using engine coolant and the radiator to cool exhuast gasses, which would seem to put to use the general excess cooling capacity of most radiators anyway. NOx seems to be the biggest stumbling block for tier 2, bin 5 emissions for turbodiesels, so it's exciting to see they're coming up with simple, low cost solutions like this.

John W.

There are so many things to juggle in combustion theory: lower temperatures mean less Nox, but higher temperatures mean greater efficiencies and higher torque.

With Hydrogen augmentation and other helps, the fuel ratio can be pushed far past stoicoimetric and still keep a fast enough burn rate/mixture, but when past stoiciometric the temps drop off again, reducing Nox and getting better mileage at the same time because it's way leaner than normal. There are people doing this on the sidelines now.

The sooner we go electric, the sooner all that complicated juggling and polution control in the I.C.E. will be done away with. I guess this EGR cooler is a good thing in some ways, but I just look forward to the day when it will be obsolete.

Harvey D.

John W:

I agree with you. This is just one more bombshell from the dying ICE/OIL era supporters. Many more will come in the next 10 years.

Those people (and their friends) will try their best to find 1000 ways to delay the unavoidable transition to PHEVs and EVs.

OTOH, old ICE technology upgrades to reduce air polution and liquid fuel consumption are welcomed. A gas/carbon tax would give similar results while giving the government the badly needed extra revenues. Both would be even better.


Wasn't EGR the technique that mechanics so adored about 1970 - you drove an hour, the mechanic worked two hours, then you could drive another hour. It worked so well everyone abandoned it.

This is undoubtedly far superior and all computer controlled so nothing will go wrong, go wrogg, gno rwonk...

allen Z

You're a riot.
We could do this refined recirculated gas system along with advanced combustion engines in the 50-60+% efficiency range.

Sid Hoffman

Umm... no. EGR is still widely used in tons of cars today. You just don't hear about it because it's reliable enough that no one even knows it's there any more. Besides, as the article states this is mainly for diesel engines which run ultra-lean by nature and also have extremely low exhust temperatures compared to gasoline, thus making EGR and turbochargers last longer and more reliable due to the lower heat exposure.

Rafael Seidl

Cooled external EGR, as shown here, is only useful for diesel engines. Virtually all turbodiesels designed in the last 7-8 years feature this technology, to meet tightening European NOx emissions standards without expense exhaust gas aftertreatment. Levels of 30% and more common for certain operating points of LDVs, for trucks only 10-15% are feeasible.

The additional tweak presented here permits further reductions in NOx production during initial warm-up (relevant for the emissions certification) and for prolonged idling / very low load.

EGR is also used in some gasoline engines, though it is internal (negative valve overlap via cam phasers). The results is 4-5% better fuel economy in part load due to reduced throttling overhead. After all, EGR reduced the apparent displacement of the engine.

As for all of us switching to electric cars: the hurdle is not so much consumer acceptance (hybrids are selling briskly) but the sheer cost of the batteries or fuel cells + hydrogen infrastructure. If someone comes up with an all-electric drivetrain with adequate performance and range at acceptable cost, the ICE's days will indeed be numbered.


Raf- Only on recent vehicles with variable Cam timing capabilities on at least the Exhuast side omit EGR and induce reverse flow without the need for an EGR valve to pipe exhuast back into the intake manifold. Vehicles which still do not have the capability to adjust cam timing on the fly still use EGR valves and have a pipe connecting an exhaust port (and the exhaust manifold on older vehicles) directly to the intake manifold through a valve controlled by the ECU. EGR is used mainly during part load operation.


Well I was having fun with the EGR bit.

I wasn't aware they got it working well and it survives. Thanks to Sid, et al. for the facts. As always, I hope IC thrives.

After battling with the EGR of 30 years ago my mechanic became a Maytag repairman.


Virtually all gasoline engines use cooled EGR. It is blocked on heat-up, and on warmed up engine EGR rate goes to zero at idle and at full power. Thus draw backs of early EGR is eliminated. EGR reduces NOx generation by up to 30%, and three way cat is doing the rest. Additional benefit is slightly reduced fuel consumption at partial load (due to less pumping losses), but it is way less then 4-5% referred by Rafael. Passive EGR is not widely used, because remaining gas is hot and not so effective in NOx reduction, plus hot gases cause problems with engine wear and fuel consumption (relevant to diesel engines too). I had troubles with EGR too: on 2.5 l Mazda engine because of troubles with closed loop operation at full throttle engine worked with over rich mixture, and resulted soot clogged EGR valve. While fixing this problem, I doubled EGR as anti-theft device. Magnetically operated switch shorts EGR valve, and EGR stays open at idle and start-up. Engine immediately dies, and no computer diagnostic could reveal the problem.

On turbocharged diesel engine EGR is very complicated matter. Diesel exhaust contains soot, and if cooled exhaust gases are recirculated to air intake before turbocharger, soot/oil mixture precipitates on compressor blades, disbalances them, and resulted vibration destroys compressor. Because of that diesel engine manufacturers usually route exhaust gases (sometimes filtered) after turbocharger, but this requires very sophisticated control of turbocharger (usually done by variable geometry turbocharger). Interesting enough, appears that this fundamental problem disappears right now. Due to current extremely high requirements for soot emission from diesel engines, exhaust after properly working diesel particulate filter is virtually free of soot. Thus it is possible to use for recirculation this exhaust stream and feed it directly before turbocharger.

Rafael Seidl

Clearly, Europeans design their engines a little differently than Americans do. Cam phasers are fast becoming standard issue on spark ignition engines here, even for subcompacts. Fiat and others do achieve 4-5% improvement in fuel economy because of internal EGR.

Sophisticated cylinder honing techniques and additive formulations have increased oil change intervals to 15.000-30.000km (or 12 months) for LDVs and >100.000km for HDVs. Compressor failures in diesel engines due to contaminated EGR are rare.


Diesels with EGR introduce SO2, water & Carbon (soot) back into the combustion chamber. Anytime you add sulfuric acid & dirt into an engine you limit its durability. Take the exhaust gas from AFTER the diesel particulate filter & eliminate the sulfur & soot. Variable valve timing is now standard on most diesels too.


To Andrey

I have a 1996 Honda Civic, with the D16Y7 motor. There has to be over a million of these on the road (1996-2000, same generation). This motor does not have EGR. People are always surprised about this.

Tim H

Clearly, the problem is related to the proper regulation of hot air. A Harvey D./Broken Record tax on repeating the same tired mantra over and over about carbon taxes should make the hot air issue palatable for the general public.


Every week new readers of this web site post same questions and ideas already grinded here two weeks ago. Some regular posters have stamina to answer their questions and drive home their ideas again and again. I don’t. Relax, man.

thomas ricks

My personal views of fuel cell transportation is that we depend on fuel to much.we need to reach out and find the next new thing to replace fuel ,its not hard its right in front of us , we just cant and dont want to find it.if you could fill your car up and it last you 30 days will that be remarkable.the tecnology is all around us if we stop bein greedy {corporat world} and stop pricing these car so hi ,and work together.if i had the money I would put my idea to work but until then goodluck ps work together


How about forget the egr and make it a 6-cycle? Change the cams to allow one up and down stroke with valves closed and a dedicated direct injector of water at or around TDC - maybe even keep the turbo but have less heat issues. Dunno, just something I read on the all-knowing 'net.


I'm not sure TRMC's new cooler would work on a big (6.0L+) diesel, the performance loss would be unacceptable to the American heavy duty diesel truck buyer -- you know how we are.

Ty D.

I've been diesel tech. for over 10 years now and have many experience with Tokyo Radiator Manufacturing (or TMRC) through their usage in heavy duty diesel DT and MAXX engine and found power and performance has never been an issue on engine with TMRC system even on fully loaded trailer or bobtail as long as cooler cores can tolerate extremely hot operating condition eliminating possible coolant leakeage to combustion chambers.

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