So Borg-Warner's been working on a clever way to run a gasoline turbo engine called Valve Event Modulated Boost, which is a dumb name for a cool concept.

Basically they divorce the two exhaust valves, sending the high-pressure first half of the exhaust stroke to the turbo thru one valve, and the scavenging-sensitive second half directly to the cat thru the other valve. Fecking genius!

Green Car Congress: BorgWarner suggests Valve-Event Modulated Boost system can offer 6-17% fuel economy benefit over already downsized and turbocharged engines



Best of both worlds -- the turbine gets all the pulsey spooly blowdown energy and then is sealed off from influencing the engine's valve overlap.

More info in SAE papers 2010-01-1222 and 2012-01-0705. The upshot is response, emissions, engine delta p, bsfc... it all improves. The fact that boost can be regulated by adjusting overlap between the two exh lobes (no wastegate needed) is basically a footnote compared to the other benefits...

There are few issues to overcome (cost of the fancy concentric exh cam needed, perhaps turbine inlet temps, some packaging) but I bet we'll see VEMB in a production car within a few years.

 

Very cool.

 

So what you're saying is you're going to have 2 exhaust valves per cylinder and instead of using both of them you'll use one and then use the other one? Doesnt seem too efficient.

 

@triple88a, with a turbo engine, it actually winds up more efficient to run the exh valves sequentially like this. It's easier for the piston to shove the exh contents out against low pressure instead of high pressure, so there's less pumping work. VE improves for the same reason (less backpressure during overlap).

For sure, some increase of exh valve diameters will need to happen with VEMB. Gotta redesign the head anyway to divorce the exh ports...

 

Neat concept I admit, except for the EGR gunk in my intercooler, but that's just me being silly.

Sounds like a great application for Garrett's axial turbocharger.

 

This Borg/Garrett competition reminds of the mustang/camaro rivalry.

And we will be the ones to reap the benefits

 

emissions...


if they would quit dicking with all of these gasoline motors and apply some of this tech to diesel, we would be moving forward in a more efficient way IMO...

 

I can believe fuel efficiency, I can buy spoolup assistance, but in terms of peak power you'll never make up for the fact that you're effectively losing half of your exhaust valve area. At least, not unless there's a clever way of doing variable duration camshafts so that at high revs you can just have both valves open like you would on a normal engine.

Of course, it's likely to be combined with an undersized OEM turbo that's choking off flow at high revs anyway, so perhaps for OEM applications that just doesn't matter.

--Ian

 

The answer is MOAR BOOST.

 

They run both exh valves open at the same time at high engine speeds/loads. This is how boost is controlled actually, they increase overlap between the blowdown valve and the scavenge valve to divert exh flow to the (low pressure) scavenge manifold.

The VEMB setup does lose a bit of exh dwell at full lift though. They upsize the exh valves in this study by I think 1mm to compensate.

Power-wise, in the SAE paper they show that VEMB's reduction of retained exh gas in the cyls improves combustion phasing, in turn allowing an increase of compression ratio by 2-3 points. This is in addition to the VE gains and pumping loss reductions.

I'm with TurboTim, the pulsely nature of VEMB would be ideally suited to the Honeywell DualBoost turbo.

 

That is always the answer.

 

Does that mean from 11 to 11.3:1, or 11 to 14:1??

 

Whole ratios. So 10:1 becomes 12 to 13:1.

 

Thanks...that made it all click.

This coupled with direct injection would be full of win.

 

That's huge... and tickles my BS meter. But hey... maybe real world you'll get +1, which is still a lot.