NGV vs. Petrol

facts, natural gas in commerical quality is better because:

It has less than 1 ppm water

It has consistant composition

It has higher octane number

With 99% of the molecules smaller than 4 carbons, it burns more completely

It has less sulphur

I run lots of Nat Gas engines. We rebuild heads after 3 to 5 years and whole engines every 5 to 7 years. They run at 75% to 100% loaded 24/7, only downtime is to change fluids, spark plugs and some in spections.

I don't have experience to comment on octane numbers but I thought the loss of latent-heat cooling was significant in running temperatures. Watch your exhaust valves.

True, if you want high BMEP, ie high horsepower engines with small displacements. NG is not a racing fuel but turbo charging to 25 psig or running 10 to 1 compression ratios is OK

I worked on instrumenting a Sierra pickup converted to NG by SAE club engineering students.

350cu-in engine with Corvette heads, multi point injection and 14:1 compression ratio. If I remember well, the result was 350BHP.

Back then, the F1 injectors used were quite leaky for 100psi NG. Not quite roadworthy. The smell made us fear sparks...

Converted it back to a throttle body mixer and modified the regulator to add servo electronics in order to compensate for temperature variation problems in winter. Without it, driving in and out of heated parking lots was problematic.

A good adjustable electronic ignition is needed to provide sufficient advance.

where did you get pistons/heads to achieve 14 : 1. At that ratio, the methane would detonate and you'd have broken fordged rods. 12:1 is available and would work on methane and 100 to 105 octane fuels

Don't ya love it, ignition BTDC

It's the only way to go!

I am citing out of memory, I may be wrong on this.

This is from a report on the 1991 competition.

I worked on a further modified vehicle using multi point injectors.

The report on the 1992 competition has on pages 14 and 15 a compendium of the vehicle modifications. Stated compression ratios vary from 9:1 to 14.7:1.

Nice report, the OP should use it. An exerpt says this:

The trucks that were successful in earning points in the emissions scoring had an average compression ratio of 11.5:1. This ratio is slightly higher than the overall average of 11.3:1 and is a full 2.3 points higher than the stock gasoline engine. This increased compression was obtained by reducing combustion chamber volume

In table 1 the CR ranges from 9.6 to 1 to 12.5 to 1.

Table 1 spans on two pages, the 14.7:1 in on the first page.

my appologies then.

Hi Lenman, In India we have thousands of Vehicles running on N.G there is no problem.Also NG is localy produced here so no increase in price and no plloution. Suresh.Sharma.

Of course there is pollution when burning Natural Gas, maybe not quite as much as diesel or petrol, but still pollution as it is NOT carbon neutral!!!!!!

I think the valve life is shorter when using NG compare by using petrol, because of burning temp of NG is higher than petrol. Is that right?

Most valves are sodium filled anyway so there probably is no problem but the valve seats may incur some damage if not spec'd for the heat range of the fuel.

We used Stellite valve seats with butane/LP/NG and various fuel and never was any trouble had from high heat.

That mean I must change certain part in the engine block to make sure everything goes well, when I am using NG. Tq for the info.

Mean you must check and see if the part in the cylinder head; noun name "valve seat" is sufficient for intended fuel usage.

Does NGV actually burn hotter than petrol (or even diesel)? i would be really interested to know.....

you get less cooling on the intake because there is no heat of vaporization of the fuel.