@gor,
This can be a good idea, and is done with private money.
Having separate engines, one for each type of fuel, allows for optimization of an engine to the specific fuel type in order to obtain the most fuel efficiency and durability. For example, NG engine requires modifications to the valves and valve seats, valve timing, fuel injection system, ignition system, compression ratio, lubricant, etc.

A typical family sedan having 2.4-liter engine and 150 hp engine can now have 2 engines of 3-cylinder 1.2-liter each, each engine producing 75 hp. Running on only one engine at a time, the operator will see a significant gain in fuel efficiency as the result of engine down-sizing alone, because the small engine can operate closer to its peak efficient point. The increase in weight and cost will not be much, and will be recuperated from savings in fuel efficiency and fuel cost. Purchasing price could be somewhat less than that of a gasoline-electric hybrid, and a lot, lot less than the purchasing price of a PHEV. However, the city mpg gain will be less than that of a HEV or PHEV due to the lack of braking energy recuperation.

According to the referenced patent, "The selector control actuates a transfer system that prevents simultaneous operation of both engines." This can and should be modified to allow simultaneous operation of both engines upon pushing the gas pedal more than 1/2 way down, in order to maximize power potential so that performance will not suffer.

Shouldn't cause too many problems as long as it automatically reverses at full throttle.
I think someones 'havin a lend'.

Try to design a 4-cylinder 2.4-liter family sedan to run on both NG and gasoline to see how efficient can you run on NG with that engine, vs a 3-cylinder-1.2-liter engine optimized to run on NG.

You need to be able to operate when one or the other fuel tank is empty.  Try to design a 1.2-liter engine which meets your performance targets and emissions when your vehicle normally gets a 2.4-l.  Don't forget that you'll have cold starts every time you switch one on, which will be an issue for emissions.

There have been a great many schemes for variable compression, from hydraulically-movable piston crowns to eccentrics which shift the crankshaft to an engine block hinged on the crankcase.  I'm sure that it is cheaper to use one of these rather than building two separate engines (two crankshafts, 4 camshafts, extra balance shafts...).  If you do that, you also get the capability of running with any CR between the limits, not just two values.  That allows optimizing the geometric CR for variable fuel mixtures (e.g. FFVs) and anything that varies the air charge, such as boosting or Atkinson/Miller valve timing.

So long as NG is much cheaper than petroleum, I expect that most users would go for a dual-fuel engine tuned for 87 octane and simply eat the cost of lower efficiency.

On reflection, trying to understand the possible benefits.

In a stationary application or maybe marine application when emissions in port are important or similar - then one may be able to gain a parts count reduction from generator or other load device and associated cost advantage or improved reliability robust dedicated single fuel engine. Or when fuel supply or costs are problematic.

It may be advantageous in order to meet appropriate technology status such as a hospital generator in some (lucky) third (or majority) world where fuel supply or costs fluctuate wildly.
To the point where it gets so bad you ordinarily need a backup engine.
( I hate to think of the fuel quality in that situation and may go back to the start with higher tech filters, fuel analysis and adaptive combustion strategies variable comp/timing multiple injection events via the various current strategies.
YES YES YES.

But for the application described it is bringing almost every problem we have with ICE, from GHG fuels to weight to the implicit lack of versatility that have been identified and strategised by mainstream manufactures for the last 10-20 years.

Implicit is the inability of the design team to overcome the fueling problem.
While all manufactures find adaptive fueling problematical and insiders will level that 'it' is more serious than they let on. with too many current attempts failing in the feild.

Couldn't help but wonder:

" invented by Herns Louis, veteran of more than 30 years in the parts manufacturing industry ranging from automotive to aerospace, specializing in computerized parts machining."

There is a lot of 'work' in this one.

Roger,
That is all well and good, minimal pumping losses suggest better fuel economy than cylinder deactivation and starting with a specific fuel dedicated engine will help too with the bonus of potential to achieve simplified technology and hence maintenance which is incredibly important and easily overlooked.

Where it fails is that in the LDV app there is a complete duplication of the fuel system adding development cost, serious weight penalty from duplication complexity and taking up the already limited available space.
For what end?

Primarily to gain an economic advantage for the spot price of different fuels.

That may interest (and should) the bean counters but make it difficult for everyone else. That duplication will - history shows - be expensive to provide.

The upfront costs will need to be justified I.M.O. there needs to be a priority need for any combination of the advantages related to necessity of having multifuel ability.

Where the fuel supply may change I.E. a mine where diesel is required (but expensive) and gas will become available then it should be able to swap out even the diesel and run gas in both allowing fast changeover without touching the powered devices.In this instance dual fuel diesel ignition gas engines are available and could run varying proportions.

There is no prospect of paired running being advantageous as the shaft power required to run heavier loads ocasionally suggests more losses at low power outputs.

The more I think of it the less it appeals.

I like the renewable hydrogen storage prospects but don't accept that even that is particularly easy, or safe as the extensive infrastructure and natural gas (methane) fuels are not greenhouse friendly.

In this world homo economicus has created,sadly, the lowest common denominator will prevail.

IMO the electron will prove to be the most efficient and suitable at least in L-M.D.V.