India’s first 100 per cent dimethyl ether (DME) fuelled vehicle for on- and off-road applications has been developed, initiating a new chapter in the quest for a sustainable alternative-fuel transport system.

DME is renewable, can be produced indigenously, and several countries like Japan, the US, China, Sweden, Denmark, and Korea are already using it to power their vehicles. However, the use of DME in internal combustion (IC) engines remains uncharted territory in the Indian subcontinent.

Businessline had on March 18, 2020, reported on a collaborative research between IIT-Kanpur and Chennai-based tractor manufacturer TAFE to develop a tractor that can run on DME. The research had received a grant of ₹1.6 crore from the government’s Imprint-2 programme.

The research has come to fruition now. Dr Avinash Kumar Aggarwal and Prof Tarun Gupta of IIT-Kanpur have developed a 100 per cent DME-fuelled engine with a mechanical fuel injection system. “It exhibited higher thermal efficiency and lower emissions than the baseline diesel engine,” says a press release.

DME has properties similar to liquefied petroleum gas (LPG), and its usage can simultaneously reduce particulate matter and nitrogen oxide emissions. It is produced either by dehydration of methanol or from syn gas (a mixture of carbon monoxide and hydrogen). However, DME cannot be used in an unmodified diesel engine in higher proportions.

The newly innovated DME tractor is said to be a cost-effective and eco-friendly solution for agricultural applications. In addition, the simplified engine technology, which does not require expensive and hard-to-maintain emission control devices, is user-friendly, and compliant with stringent emission legislations. The exhaust from the DME-powered tractor is smokeless, thereby preserving ambient air quality.

DME-friendly design

The DME-fuelled engine emitted extremely low particulate and soot emissions and almost no smoke, even without expensive after-treatment devices, making it a viable alternative fuel and engine technology adaptable to the conventional diesel engines used in agricultural and transport sectors.

India’s oil import bill and greenhouse gas (GHG) emissions can be reduced by converting vast domestic coal reserves, low-value agricultural biomass waste, and municipal solid waste into methanol and DME for a variety of applications, including powering tractors and other vehicles.

It was found that certain additives enhanced DME’s lubricity. DME-compatible materials were used in the fuel injection equipment (FIE) — fuel supply and return lines — developed by the IIT-Kanpur researchers. Customised DME tanks were developed. The researchers used 3D computational modelling to determine the optimum FIE system design for DME induction. They then studied DME’s macroscopic and microscopic spray characteristics using high-speed imaging and phase Doppler interferometry (PDI). Based on these results, a dedicated FIE was developed for the DME-fuelled engine prototype. The DME engine was tested under full throttle performance (FTP) and part-throttle and part-load (PTPL) test conditions.

The DME-fuelled engine exhibited higher brake thermal efficiency. It produced negligible soot while significantly reducing hydrocarbon, carbon monoxide and carbon dioxide emissions. The results have been published in journals such as Energy Conversion and Management and Fuel. The engine prototype was installed in a tractor and successfully operated by the industrial partner, TAFE TMTL, Alwar, the release says.

DME vs DEE

Even as the DME technology is coming within reach, scientists are suggesting its sister — diethyl ether (DEE) — as a better alternative as it more resembles mineral diesel and can be more easily blended with diesel. This, in turn, would necessitate less tweaking of the existing engine. Dr Aggarwal has produced a scientific paper on DEE (published in Fuel magazine), too, which says that DEE requires merely recalibrating the fuel injection system.

DEE is an isomer (or another form) of butanol. With four carbon atoms and one oxygen atom, it belongs to the category of ‘oxygenated fuels’, which reduces carbon monoxide and soot emissions due to its shorter carbon chain and better ignition properties.

“Compared with mineral diesel, DEE’s most remarkable properties include a higher cetane number (>125), lower auto-ignition temperature, acceptable energy density, and wider flammability range,” says Dr Aggarwal in his paper. DEE has long been used as a cold-start performance improver for diesel engines. It is commonly used as an ignition improver for diesel engines since it thoroughly mixes with diesel.

More importantly, DEE is a renewable fuel if it is synthesised from ethanol, and is produced from low-value biomass feedstock through dehydration.

Dr Aggarwal also points to a flipside of DEE — its higher volatility increases the chances of ‘vapour lock’ in the fuel injection system. However, it is a promising green fuel.

In sum, both DME and DEE are vastly superior to mineral diesel.