renewable fuels

Effects of Renewable Diesel Fuels on Combustion, Emissions and Engine Performance

Research into new renewable fuels indicate that bio-diesels provide better performance and lower emissions than either traditional diesel or petrol.

Even before carbon-driven climate change was a hot topic, diesel was getting a bad press. Concern about emissions was justified, but objectivity was often lost amidst the rhetoric. The level of nitrogen oxides and particulates produced was (and still is) unacceptable, but “diesel” isn’t inherently bad. Well-designed diesel in well-designed engines may be the answer rather than the problem.

The need to reduce CO2 for climate reasons and the need to reduce traffic fumes for health reasons are two different issues. On average, diesel is more energy-efficient and produces less CO2 than petrol. That’s why governments encouraged the public to go diesel in the first place. The health risks lie in the levels of NOx and non-combusted particulates and aromatics produced by today’s diesel vehicles.

However, diesel fuels are very easy to produce from waste and renewable natural sources. Growing those sources absorbs CO2, offsetting that produced from burning it. Running vehicles on renewable fuels can make a major contribution to carbon reduction. Moreover, diesel is not a single chemical but a variable formulation. The levels of harmful side-products in the exhaust depend greatly on its production process, additives and the vehicles that use it.

Developing Renewable Fuels

Testing any fuel requires specialist expertise and precision. Supplies must be scrupulously consistent, and the effects of varying them assessed under an exhaustive range of different conditions. There can never be a single objective – nothing is gained from producing a clean fuel that is too viscous to pump, damages engines or won’t ignite in cold weather.

Research into the exhaust products of chemically similar diesel and bio-diesel has yielded exciting results. They confirm that diesels combust at a lower pressure, generate less heat and provide lower fuel consumption, but better still bio-diesels produce less “soot” and nitrogen oxides than expected.

Bio-diesels produced in different ways give different results, but the majority compare very favourably with traditional diesel and other fuels.

Promising Results

A study from North Carolina University compared six biofuels against traditional diesel (“FAME”) and jet fuel. The bio-diesels included batch deoxygenated fatty acids derived from canola (DCFA), a similar diesel produced by continuous deoxygenation (CDCFA), a hydrogenated batch-produced variant (DCFAH), a batch deoxygenation of lauric acid (DLA) and isomerised fatty acid alkanes (IPCF).

The renewables left more hydrocarbons in their exhaust, but all other waste products were lower (particulates, sulphur, CO2 and NOx). More complete combustion and even lower NOx can be obtained with appropriate additives and engine re-tuning.

Renewable diesels must also be tested for their effects on the injectors, filters, hoses and gaskets of older engines. However, these are relatively easy to remedy with additives or straightforward upgrades to existing components.

The research shows that bio-diesels can deliver the fuel economy and low carbon emissions of traditional diesel and rectify its shortcomings at the same time.

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