Valve Event Modulated Boost
#1
Valve Event Modulated Boost
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.
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.
#4
@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...
For sure, some increase of exh valve diameters will need to happen with VEMB. Gotta redesign the head anyway to divorce the exh ports...
Last edited by JKav; 07-31-2012 at 06:11 PM.
#8
@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...
For sure, some increase of exh valve diameters will need to happen with VEMB. Gotta redesign the head anyway to divorce the exh ports...
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
#10
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.
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