Power Loss Using Biogas Instead of Diesel

What advice can the engine's manufacturer offer?

Haven't asked yet.

I thought this would have I simple answer, but I guess I don't get to the problem the right way.

Here are the engine specifications by the way:

http://www.yanmar.com/store/item.asp?ITEM_ID=52&DEPARTMENT_ID=62

<...Haven't asked yet....>

I think the error was that I took the mass ratio and made the supposition it was volume ratio...

I'll come back to you with the results

The engine will be destroyed in a few minutes from etreme detonations of the gaseous fuel. The only way to refuel a diesel is to use the diesel fuel as ignition source (as is) and meter the bio-gas into the intake manifold as a co-fuel. Power output can be then modulated by metering in more or less bio-gas.

basically the fuel air ratio is by weight

a unit of biogas takes up much more volume than liquid diesel fuel

that displaces a portion of the intake air, resulting in less air, and then less fuel by weight.

the power can be restored by turbocharging or supercharging to return the charge rate to normal.

probably not practical at your scale.

probably a larger engine running NA is the most practical solution.

I see a problem is the cylinder displacement volume. Which remains constant @ 0.219L and Energy content ratio between Diesel to bio gas is approx 38.6MJ/L to 10MJ/L.

Though we use correct Fuel to Air ratio, to get the equivalent power achieved by using diesel the cylinder volume will have to be increased almost 4 times for Biogas because the energy content of Biogas is lower.

Regards,

Hemant

Hemant - pls see my #5. Energy content of bio gas is not 10MJ/L. If it's 10 anything it's 10 MJ/m³, and that would be low quality biogas.

As you say, the cylinder displacement volume remains constant @ 0.219L. Whatever fuel is used, it is necessary to add the right amount per stroke for the oxygen in 0.219L. As other posters have said, it's not practical to convert, but in principle, if the compression ratio were reduced from ~ 20 for the diesel to 8 - 10 for biogas (change cylinder head), replace the injector with a spark plug, and fit an appropriate gas carburettor, I don't see why it wouldn't work. But it would be cheaper to get another engine!

Cheers.......Codey

Biogas cannot auto-ignite without the pressence of diesel. 10% of diesel is the required amount of diesel necessary to assure a proper combustion.

In fact we can just add the biogas in the air intake. For farmers who can produce cheap biogas, il would mean some savings as they would produce their energy as much as possible with the biogas they produce and not from diesel.

To inject the biogas in the intake though, I will have to design a carburetor to make sure I have the right proportions in my engine.

As I mentioned in another blog, with an almost exactly the same theme, it would be a good idea to remove the injector, make up an adapter for both this injector and another one for gas and screw them both into the cylinder head.

That way you still get the maximum amount of air (no dilution from the gas) into the cylinder as before, but now you can inject your gas under pressure. Also at the right time, the diesel for ignition.....

Naturally a Turbo would benefit things even more as you can get more air in and therefore burn more gas fully and completely...........but your motor must be reconfigured to allow a Turbo. For example, the piston crown needs extra cooling, the usual way is at least one jet of lubrication oil (sometimes 2), aimed at the piston crown, but from below.

You may need an uprated oil pump to allow full/normal oil pressure AND piston cooling.....

Also I would recommend "Long Life 3" Synthetic oil, this lasts and lasts and just evaporates away if driven too high in temperature, without developing ash or other products of combustion.....

Hi,,,,

As the energy content ratio of diesel to Biogas is 4:1 you need to increase the fuel quantity by same ration and so the oxygen (Air) for combustion, to get the same level of power.

i.e in case of Bio gas we will need to have 4 time the volume of fuel and air mixture then required for Diesel. Hence, cylinder volume seems to be an important issue.

Off course , fuel injection system, compresion ration and ignition system needs to be adjusted according to fuel type used.

To me it seems that this conversion would be like making a complete new engine.

Off course , fuel injection system, compression ration and ignition system needs to be adjusted according to fuel type used.

to realize the economy you may change the gearing instead or would adding a turbo-charger be appropriate?

Hi,

Well the idea is to minimize the change. So if I need 50 kW maybe having a 75 kW engine functionning with biogas (instead of diesel) would be enough for my needs.

It would require buying an engine of more power to use "partially"

You see a disparity NG vs. biogas?

Not really. The major difference between Natural Gas and Biogas is the higher Nitrogen content. If an engine has been converted to NG it would also work on Biogas with a little tweaking of the injector size and mapping. We use such engines in the UK on sewage treatment works to generate electric power to run the motors on site and the heat maintains the bio-digester at temperature and heats the offices as well.

Dear Markmai86,

There are ready unit available in the market, check this website http://www.greenpower.cn/P-generator-08.htm

this manufacturer offer flexible selection of gas fuel engine ( Biogas, Natural Gas, Propane, LPG etc ) and the engine can be mount on various type of machine like generator, lawn mower, water Jet cleaner, or water pumps.

Just a little side note: The energy of Diesel is near 42.5 to 43 MJ/kg. I prefer to use this number rather than the caloric value per Liter. It avoids the mistake you made in your calculation. The stoichiometric ratios are based on weight not volume as already pointed out.

If you do the same with the gases applying their specific gravity and their heat content per kg your numbers will be right.

Thank you for the information.

I guess you can just use PV=nRT and n=m/M to convert gas volume to gas mass?

No! you can't. Those equations apply to gases - if you know the molecular weight you can calculate the density. E.g. oxygen has MW 32. Molar volume = 22.4 m³ at 0°C and 1 atm, so density of oxygen at those conditions = 32/22.4 = 1.43 kg/m³.

Floram was referring to liquid diesel. The ratio of your 38.6 MJ/l to his 43 MJ/kg is the density, ~ 0.9 kg/l. I thought it was a bit lower than that, but that doesn't affect the principle.

Cheers.......Codey