Issue: Apr 2010


by Bob Brooks

Detroit, MI: New information and comment by combustion experts at the recent SAE Congress meeting here provide substantial reasons to believe critical fuel combustion could be the first fundamental combustion advance for IC engines in a very long time. Large gain in fuel efficiency, decrease in engine out emissions and multifuel capability have been demonstrated with commercialization under way.

Chris de Boer, VP R&D, Transonic Combustion, Camarillo, CA, explains that liquid motor fuel catalyzed and brought to a critical state at temperatures above 700F and pressure of 200 bar in the firm’s unique injectors, converts instantly into a gas and ignited by compression heat. Released into IC engine combustion chambers at top dead center of piston travel, combustion quality provides a remarkable range of advantages. (de Boer was recruited from Ricardo)

Critical fuel combustion engines can intake gasoline or diesel fuel or any mixture of both along with alcohol additives for operation at 16:1 compression ratio with major fuel efficiency and emissions gains. Very fast fuel burn takes place before reaching combustion chamber walls thereby reducing thermal losses. Efficiency is further enhanced by ability to operate unthrottled lean, misfire free out to 80:1 air fuel ratio. HC, CO and particulate emissions are cut to insignificant levels. EGR rates up to 50% with stable combustion are achieved with very low NOX levels. Combustion experts believe this will permit operation with very little if any exhaust aftertreatment when the system is optimized.

Illustrating the promise of IC engine critical fuel combustion, demonstration of the Transonic system applied to a 2.2L 3200 lb gasoline car increased highway fuel economy to 65 MPG FTP unadjusted (51 MPG adjusted). Transonic data compares this with 41 MPG adjusted highway for the VW Jetta TDI and 48 MPG for the Toyota Prius. Needless to say, if the critical fuel vehicle uses diesel fuel instead, higher fuel energy content of about 10% will add accordingly to MPG.

de Boer puts the cost of Transonic critical fuel system at about $1000 for a 4-cylinder engine. Unknown, however, are cost saving offsets from reduced Otto emissions controls. If applied to current diesel engines, even larger offsets from complex diesel emissions controls and very high pressure diesel fuel injection can be realized. .

de Boer says Transonic is adequately funded for planned production of its critical fuel injection system as an engine and auto industry supplier. He says our plan is to be
a manufacturer of the system which will not be licensed to others to which he adds that volume production is targeted for start up in yr 2015”. Three car makers are coincidentally considering use of the system. AUTOMOTIVE INDUSTRIES has learned from industry sources that a major diesel maker is tracking the development; key incentives are reduced emissions control cost and complexity and multifuel advantage.

Transonic reports 3 patents on its system have been issued with 13 more pending. Numerous proposals were made in past years for heated injection systems one of which was termed by Eaton Corp. in the mid 1980s as hypergolic combustion. The Eaton effort failed at the time, however, due to formation of deposits from the heated fuel in the injectors. A Transonic patent states this problem is solved by catalyzing fuel in the injectors and by unique design of the injector pressurizing ram and nozzle and direct drive shaft which flush out deposits.

Surely impacting car makers will be use of critical fuel combustion in combination with other engine efficiency improvements such as variable valve operation and host of other refinements. de Boer suggests that the transonic system without hybrid technology will challenge current hybrid vehicle fuel efficiency.

Another aspect is the impact on emerging bio fuel producers who must judge the future demand for middle distillate vs. gasoline type fuel if critical fuel combustion engines become mainstream. In this connection, it will be interesting to learn vehicle operator reaction to the prospect of being able to choose gasoline or diesel fuel at the retail pump. In turn, as critical fuel vehicles come into widespread use that can accept fuel with lower octane and cetane values, comes the question of whether a new fuel grade might evolve.

As a factor in the overall fuels issue, it can be argued that rather than billions of dollars in U.S. tax credits spent on ethanol to cut emissions and foreign oil, these objectives could be better achieved by tax credits for use of critical fuel combustion. On balance it would appear that existing light vehicle diesels fitted instead with critical fuel combustion technology may be the earliest to reach the market due to their existing high compression, robust architecture. de Boer suggests that IC gasoline engines intended for use with turbocharging also have robustness suited to high compression critical fuel operation.

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