Effect of biodiesel on fuel injection systems
Introduction
This page reproduces information found in the Joint Fuel Injection Equipment Manufacturers Statement, a study by the following manufacturers into the effect of biodiesel (aka FAME) and associated impurities on diesel fuel injection systems.
- Delphi Diesel Systems
- Stanadyne Automotive Corporation
- Denso Corporation
- Robert Bosch GmbH
Contents
Biodiesel and impurities
| Fuel Characteristic | Effect | Failure Mode |
|---|---|---|
| Fatty Acid Methyl Esters (general) | Causes some elastomers including Nitrile rubbers to soften, swell, or harden and crack | Fuel leakage |
| Free Methanol in FAME | Corrodes aluminium & zinc Low flash point |
Corrosion of fuel injection equipment |
| FAME process chemicals | Potassium and sodium compounds Solid particles |
Blocked Nozzles |
| Dissolved water in FAME | Reversion of FAME to fatty acid | Filter Plugging |
| Free water in mixtures | Corrosion Sustains bacteria Increases the electrical conductivity of fuel |
Corrosion of fuel injection equipment Sludging |
| Free glycerine | Corrodes non ferrous metals Soaks cellulose filters Sediments on moving parts Lacquering |
Filter clogging Injector Coking |
| Mono- & di-glyceride | Similar to glycerine | |
| Free Fatty Acid | Provides an electrolyte and hastens the corrosion of zinc Salts of organic acids Organic compounds formed |
Corrosion of fuel injection equipment Filter plugging Sediments on parts |
| Higher modulus of elasticity | Increases injection pressure | Potential of reduced service life |
| High viscosity at low temperature | Generates excessive heat locally in rotary distributor pumps Higher stressed components |
Pump seizures Early life failures Poor nozzle spray atomisation |
| Solid impurities | Potential lubricity problems | Reduced service life |
Ageing products
| Fuel Characteristic | Effect | Failure Mode |
|---|---|---|
| Corrosive acids (formic & acetic) | Corrodes all metallic parts may form simple cell |
Corrosion of fuel injection equipment |
| Higher molecular organic acids | Similar to fatty acid | |
| Polymerisation products | Deposits especially from fuel mixes | Filter plugging Lacquering formation in hot areas |
Considerations for homebrew biodiesel
The document emphasises the need to produce a good quality fuel to run in your vehicle.
Complete conversion of vegetable oil into biodiesel will ensure minimum Free Fatty Acid and mono/diglyceride content (partly converted vegetable oil molecules, which are responsible for any white layer in 50/50 soap tests).
Water washing will remove Methanol and Glycerine, as will Methanol recovery, settling and Dry Washing.
Many biodiesel homebrewers will have seen reddish drop-out in their fuel when mixed with mineral fuels, as highlighted in the Polymerisation products row above. If mixing is required, it is advisable to do this outside of the vehicles tank, and settle for at least 24 hours prior to fuelling.
As most homebrewers use their fuel within a short period of time after production, most of the negative effects of aging are never seen. That said, be aware that contact with copper (processor pipework or cylinders) reduces the shelf life of biodiesel - even small PPM copper content will act as an oxidisation catalyst for the fuel.
