Gasoline as a “Diesel” Fuel

This past week my local filling station was selling diesel fuel at $3.099 per gallon and regular gasoline at $2.339  – that’s  32.5% higher.  A drive through town showed similar differences at several other stations.  At such such price differences it is difficult to justify the use of a diesel vehicle based on economics.  While this difference is one of the highest I have observed, it has not been unusual for the past years to see 15 to 25% differences.  But why not develop diesel engines, that is compression ignition engines, that burn gasoline with the “diesel” cycle?  Have the fuel economy of a diesel and a lower cost fuel too!

For more than a decade I have favored the commercial approach of using gasoline as “diesel” fuel and have often expressed this opinion.  Often, my wife Debbie’s opinion on diesels reinforced my belief.  When I would present of her purchasing a diesel vehicle the answer was a definite no!  The historic image of diesels and the odor and mess in fueling were at the top of her reasoning.  When I would present an alternative of a high efficiency engine with 30-40% better fuel economy fueled by “gasoline”  she would be OK with the option – even at a premium price.

There are many potential options of how to burn gasoline efficiently in a “diesel engine”  These range from HCCI and RCCI concepts to conventional diesel diffusion combustion and a variety of systems in between.  I recent years Delphi and  Hyundai have published results from their work on such a concept.  Most recently Mazda, as a true “disruptor” has announced intentions to go to production in the near future with such a concept.  Achates Power has also eluded to the potential use of gasoline in their opposed piston 2-stroke diesel concept.

Historically there have been dual fuel diesel that ran on both gasoline and diesel and Detroit Diesel successfully demonstrated compression ignition “methanol” fueled diesels in fleet demonstration in the early 1990’s, a fuel with even poor ignition properties than regular grade gasoline.  Detroit Diesel sold military engines in the 1960’s that that would run on gasoline, albeit with power loss due to fuel density, fuel injector efficiency and fuel BTU differences.  Even more impressive were the Continental multi-fuel 4-stroke engines they had mechanical devices that could sense fuel properties and adjust the fuel pump to eliminate power loss!  These engines produced similar thermal efficiency and even lower smoke in gasoline mode relative to diesel!

Today there are many improvements in technology that did not exist in decades past to improve upon old concepts or that can be applied to new innovative concepts.  Variable valve trains that can effectively provide hot internal EGR, high temperature ceramic glow plugs, common rail injectors with multiple injection, new 2-stroke technologies, a variety of coatings and ceramics to deal with fuel system wear, electric boosting assist, cylinder pressure sensing technology, many advance after-treatment techniques and electronic control systems with ever increasing speed tied to new sensor technologies.

The time has come for this.  What will be the winning concept?  Who will be the bold innovators and leaders?

 

 

 

 

 

 

2 Comments

  1. Hello Mr Bob Straub,
    I think I have an idea as to a possible solution a “winning solution”.
    Have you considered Variable Compression Ratio (VCR) for a 2-cycle Opposed Piston Engine, similar to that being investigated by Achates Power and Delphi. The VCR mechanism being within the piston crown, so that the piston crown lip’s relationship with port timing remains unchanged.
    Such a VCR piston could have range of say 12:1 for full load operation and 25:1 for part load economy operation. This VCR principal was invented by BICERA in the 1950’s and a 4-cycle version was employed by Continental in the 1960,s.
    I would interested in your thoughts on the above. Regards

    1. Dear Mr Flint
      I believe variable compression ratio (VCR) can be a valuable addition to an advance diesel whether 2 or 4 stroke and conventional crank or opposed piston, for emission attainment or efficiency/performance enhancement. It also can be a major enabler to burn low cetane fuels as gasoline or naphtha via compression ignition. Obviously there are several alternative mechanisms being considered today, it will be interesting to see which gets commercially applied. I always thought a gear-train phaser, perhaps a differential mechanism, between the cranks of a conventional opposed piston engine would be the ideal mechanism for the engine, but I have never looked into the compromises it might impose due to varied port timing. Certainly for rocker beam opposed piston engines, the variable eccentric is attractive, but offset by other limitations of the configuration. I have thought the BICERA concept most applicable to the loop scavenged 2-stroke diesel due to the simple stationary cylinder head. The Lowmann engine was an interesting variation that saw production (http://www.oldbike.eu/museum/engines/post-ww2/1951-lohmann-18cc-diesel-engine-new-old-stock-unused/), I believe it described in US patent 2,583,449. Regards

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