How does valve timing change relative to the fuel?

TeddyXY71

Well-known member
Here's a hypothetical question for those of you more knowledgable than myself. How does the timing of the intake/exhaust change to take maximum advantage of any particular fuel? Reason I ask is as follows:

With the high price of fuel I've been looking at various alternative fuels. One way of powering a spark-ignition motor that has caught my eye is gasification of biomass. In short, you can run your car on wood chips if you have a well designed, properly functioning gasifier to supply the gas to the motor. The gas is mainly made up of CO and H2. The wood (or any other biomass you use) is partially burnt with limited air, which acts to gasify the fuel. (and before anyone says anything, yes, I know the dangers of CO poisoning and the appropriate precautions) Thing is, wood gas (as it is known as) does not supply the same power as does petrol. This can be alleviated by increasing compression, often past the 12:1 mark, and by optimising the spark timing. But you still, at best will only ever get 50-70% of the same performance out of a spark ignition motor on wood gas as opposed to petrol. From what I've read, wood gas burns quite slowly, and is better at supplying slow steady torque rather than instant power. How would you then go about adjusting valve timing to take better advantage of a slower burning fuel like wood gas?? This is more like a intellectual learning exercise for me at the moment rather than a project I'm about to undertake.

Out of interest the following link shows a motor that's being run on reformed biodiesel. Similar to gasification of solids, but done with liquid fuel instead. Click on the link, then select "Ongoing H2 Projects" on the left ahnd side of the screen.

http://www.biomassenergyfoundation.org

Regards,

Teddy :)
 
I'm not sure because I know nothing about the burn characteristics of wood gas. I do know that with higher octane petrol (I'm learning to speak Australian), which burns slower but contains more energy than the low octane variants, the valve and ignition events are moved to accomodate the slower burn characteristics and to gain the benefits of the higher energy content. I can't quite work out in my head what happens when you combine slower burn with lower energy content.

I'm guessing that the burn speed trumps the energy content but exactly what that does to camshaft profile is anybody's guess.

If I really wanted to know, I'd ask one of the can grinders with a skunk-works like Clay Smith or Crower and see what they thought.
 
Look up my recent post on Model T and Model A cam timing. I'm guessing that would be pretty close. Short duration, low overlap, for low rpm use.
Joe
 
I would say a wider lobe seperation would be helpful. Trap it and let it burn longer.

Petrol has a spike in pressure and it drops pretty fast. If wood gas burns slower then you would want to trap it longer to extract more power.
I would think a MSD ignition might help also, but the wood gas might act like a lean condition and put a huge load on the electronics.
 
turbo_fairlane_200":2fdjmu4z said:
seems like it would work good on a large displacement motor that ran at low rpm.

You're spot on the money there! One of the better applications for wood gas (also known as Producer gas) is for stationary diesel generators. You can replace up to 70-80% of the diesel with the wood gas (still need some diesel for ignition)

Thanks Joe, I'll try looking up your post.

Regards,

Teddy :)
 
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