The Exige 270E Tri-fuel is a technology demonstrator built in 2008 as part of Lotus’ research to understand the complex combustion process involved in running on mixtures of alcohol fuels and gasoline, which will be important for a successful transition from today’s fuels to the sustainable, synthetic fuels of the future.
The heart of the Exige 270E Tri-fuel is a roots-type supercharger and air to air intercooler attached to the tried and tested 4-cylinder, 1.8 litre 2ZZ-GE VVTL-i engine.
The roof scoop ensures that the air-to-air intercooler works as efficiently and effectively as possible in all climates and environments. All charge air ducting has been kept as short as possible with large diameter pipes making sure that the bends in these ducts are not too tight, to the benefit of throttle response and efficiency. The Roots-type Eaton M62 supercharger is run from the crankshaft, and has an integral bypass valve for part load operation. The 2ZZ VVTL-i engine has two cam profiles, one for high speed cam and one for low.
The seamless switch point between these two cams is completely variable depending upon driving conditions and engine load. This gives the Lotus Exige 270E Tri-fuel a smooth and linear surge of power from idle speeds all the way to the maximum 8,500 rpm. An electronic drive-by-wire throttle ensures the quickest engine response possible whilst keeping the emissions as clean and as low as possible, to meet relevant legislative demands. Six fuel injectors are fitted to increase fuel flow to the engine at normal and higher engine speeds and loads.
Methanol (CH3OH) can be produced synthetically from CO2 and hydrogen. Ultimately, emerging processes to recover atmospheric CO2 will provide the required carbon that can entirely balance the CO2 emissions at the tailpipe that result from the internal combustion of synthetic methanol. The result is that a car running on synthetic methanol, such as the Exige 270E Tri-fuel would be environmentally neutral.
The great benefit of synthetic methanol is that it would use similar engines and fuel systems to those in current cars; and synthetic methanol can be stored, transported and retailed in much the same way as today’s liquid fuels such as petrol, gasoline and diesel.
Synthetic methanol also possesses properties better suited to internal combustion than today’s liquid fuels, giving improved performance and thermal efficiencies. And it is ideal for pressure-charging turbos and superchargers already being introduced by manufacturers to downsize engines in a bid to reduce emissions and vehicle weight.
Lotus Engineering’s Lotus Exige 270E Tri-fuel technology demonstrator illustrates how easy it is for synthetic methanol to be embraced over time as a future fuel for road transport.
Synthetic methanol’s green credentials arise from its potential to be CO2 completely neutral. The most likely future mass-production of the fuel is by using electrochemical techniques to combine oxygen, hydrogen and carbon:
Carbon could be sourced from carbon dioxide recovered from the atmosphere using either large scale extraction facilities or biomass. Oxygen would be taken from the atmosphere and hydrogen would be acquired through the electrolysis of water; challenges remain in the electrical power required; in a green future, this could be supplied from renewable sources, an issue already being addressed by supporters of hydrogen as a fuel
Techniques for the production of synthetic methanol are well developed and understood, although not yet at an industrial scale. An early solution would be the co-location of a nuclear or hydroelectric powerplant with a conventional power station the hydrogen generated by hydrolysis of water would be combined with CO2 from either fossil or biomass sources to make liquid methanol. In the future, large volumes of CO2 could be extracted from the atmosphere.
As well as being green, another crucial advantage of synthetic methanol is that it can be introduced relatively simply. As the Exige 270E Tri-Fuel demonstrates, only small changes to engines are required, such as:
In addition, as a liquid, synthetic methanol can be transported, stored and sold to motorists exactly as today’s liquid fuels are, with only minor modifications.
Synthetic methanol is better suited to spark-ignition combustion than today’s liquid fuels, delivering better performance and thermal efficiencies, due to its higher octane rating and better resistance to ‘knock’. As a result, it is a fuel that will benefit the motorists in terms of driving experience.
For example, the Exige 270E Tri-fuel is quicker to 60 mph from standstill and has a higher top speed when using 100% synthetic methanol fuel than with conventional petrol/gasoline. Synthetic methanol is also ideally suited to pressure charging, a trend already well underway as car makers look to downsize engines to cut emissions.
The 270E is itself a further developed version of the Lotus Exige 265E Bio-fuel, which was built in 2006. The 265E also started off as a production specification Exige S which underwent a series of modifications enabling it to run on E85 gasoline.
Four enlarged fuel injectors were fitted to increase fuel flow into the engine under normal operating conditions. Two additional fuel injectors were fitted at the supercharger inlet to increase the amount of fuel being injected into the engine under higher engine speeds and loads.
This enabled the engineering project team to take advantage of ethanol’s higher cooling effect to further cool the charge air prior to combustion, which in turn reduces the amount of power required to operate the supercharger.
The Lotus T4e engine management system (EMS) was calibrated to optimise engine performance when running on various mixes of the high-octane bioethanol fuel and gasoline. The re-calibrated EMS coupled with an ethanol sensor in the fuel system provides true flex-fuel capability.