For both environmental and economic reasons, the widespread use of biofuels in all significant markets seems certain.

—Guy Hachey, president of Delphi Powertrain and vice president Delphi Corporation

One of the challenges bioethanol poses from Delphi’s perspective is the aggressive nature of the fuel in the vehicle tank.

People often say that the biggest problem with high ethanol contents is that it is very corrosive, but this isn’t true. The biggest issue is that ethanol is hygroscopic. It absorbs water easily, which causes the fuel to dissolve corrosive salts from any available source it comes into contact with. It’s not the ethanol that is corrosive, it’s what it brings with it.

—Julie Galante-Fox, Delphi biofuels specialist

Water can come from poor quality fuel storage and distribution systems or it can be intentionally added as it is with Brazilian E100. Corrosive salts can come from a variety of sources. With E10 in the United States, the problem is not significant unless the fuel is highly contaminated, but systems running on variable quality E85 fuels must be carefully specified if durability (and warranty performance) is to match levels set for systems used with standard fuels.

One of the key design skills is materials selection, an area where Delphi’s early activity in the Brazilian market has provided useful experience. Already, all of Delphi’s gasoline fuel injection systems sold worldwide have been upgraded to deliver 100,000 mile plus durability on E25, even with realistic levels of impurities.

Stainless steels have replaced mild steels and vulnerable polymers and elastomers have been replaced with new, high-durability materials or eliminated through innovative design. Current research is focused on delivering similar reliability and safety with E85 without significantly increasing system costs.

Delphi’s bi-fuel Engine Control Module already automatically detects the ethanol ratio in the tank and adjusts fuel and spark controls to optimize efficiency. The company is also using its experience to help its customers develop new calibrations that are optimized to give excellent starting, driveability and emissions on ethanol contents of 25% and above.

An as yet confidential solution is being developed to ease cold starting with ethanol contents of 85% and above.

For Delphi, the challenges presented by biodiesels are significantly different and start at ratios as low as ten percent (B10).

Handling and storage is again a big issue. Biodiesel has the advantage of being biodegradeable so is less environmentally damaging if spilt. However, this characteristic allows the fuel to degrade very quickly, particularly if stored in moist or warm conditions. Biodiesel is also more susceptible than other fuels to the growth of bacterial content. Research has shown considerable variation in the quality of biodiesel at retail pumps.

As with ethanol, biodiesel can pick up water, which accelerates chemical degradation of the fuel. Biodiesel is also an excellent solvent, dissolving existing deposits from distribution pipes and tanks and carrying it into the tiny conduits of the fuel system.

Insoluble polymers and products of age-related degradation can lead to injector coking, filter clogging and deposits in the fuel system. It also attacks many widely used materials groups, particularly the elastomers used in hoses, gaskets and seals. Peroxides, an oxidation product formed when the biodiesel reacts with oxygen, can lead to embrittlement of some elastomers, which may also become soft or swell.

The physical characteristics of the fuel also can create problems. A higher modulus of elasticity can lead to higher injection pressures and reduced service life while poor flow characteristics occur from temperatures as high as 0°C.

Another potential problem with biodiesel is lacquering, which can occur anywhere in the fuel system. The most likely location is around high-pressure injection nozzles where the very high temperatures can cause a reaction of the organic material, leading to a build-up of potentially harmful organic deposits.

This is a considerable list of challenges for fuel system engineers. We also have to accommodate considerable variation in both physical and chemical characteristics as the fuel properties are heavily dependent on the production materials and the quality of delivery and storage.

—Dr. Detlev Schoeppe, Delphi Diesel director of engineering

Delphi is conducting an extensive international bench testing program with fuels at concentrations from B10 to B100. It is also conducting high mileage fleet testing in partnership with its customers and end users in each sector: trucks, off-highway and passenger cars / light commercials.

Currently all Delphi systems are compatible with B5 and the company is developing injection systems compatibility with significantly higher biofuel contents.

A good example of Delphi’s work is the new capacitive fuel level sensor. Traditional level sensors use a mechanical system that is particularly vulnerable to aggressive fuels. Delphi’s new sensor has no moving parts and can measure gasoline, diesel and biofuels without component or software changes, allowing a single part number to be used for all types of fuel.

Delphi currently has a range of biodiesel-related research projects. These include studies of the fundamental parameters affecting biodiesel performance such as deposit formation and aging, pump durability and performance tests, through to engine and vehicle tests in several locations around the world.

At Delphi’s Diesel Heavy Duty Technical Centre in London, a 12-liter engine pounding a typical heavy truck duty cycle is fueled by B30 diesel. After several hundred hours the advanced Delphi EUI fuel injection system will be stripped and examined, re-assembled and installed for another test period.

Heavy duty applications impose substantially greater demands on the engine than light duty. We expect our injection systems to work reliably at exceptional pressures (up to 2,500 bar from 2007) and deliver 1 million mile durability with zero maintenance.

—Delphi Diesel Heavy Duty chief engineer David Draper

Following the trial, components will be taken apart and examined for signs of increased wear in areas such as the injector pin seat and for signs of degradation to metal, polymer and elastomer components.