NOx
 

Dear readers,

Does a methanol-water blend have a more positive effect on reducing NOx-emissions than water alone?

Thank in advance.

water methanol
 

I would think not.

Nitrous oxide production is a temperature sensitive combustion product. If temperatures exceed a certain temperature NOx production increases dramatically. The addition of methanol to the mix mostly has its effect during the pre-combustion portion of the engines operation. The presense of the alcohol slightly reduces the viscosity/surface tention of the mixture so it atomizes better. It increases the evaporative cooling of the intake charge as the alcohol can continue to evaporate after the intake charge becomes saturated with water. It contributes evaporative cooling during the compression stroke (as do the water dropplets) lowering the initial combustion temperature. The methanol will actually slightly increase the combustion temperature you would have if you were running water only as it contributes some energy to the combustion process. In gas turbine engines they have determined that about a 10% methanol mix will exactly cancel the cooling of the water on the exhaust gases so they can have the same exhaust gas temperatures with or without the water injection system activated.

The presence of the alcohol does however reduce the unburnt HC in the exhaust as it promotes more effecient combustion. The peak combustion temperatures and pressures are typically lower with both pure water or an alcohol water mix, so you should also see some drop on NOx but off the top of my head I don't recall as specific research paper on the effect of the presense of methanol on NOx production.

Larry

Larry thank you for your comment.