From: Issue 32 Categories: Energy/Tech
The Science of Carbon Busting
Car and tar sands emissions combined generate nearly one-fifth of Canada’s greenhouse gas emissions, and the oil sands’ contribution will nearly triple this decade if production rises as forecast. Both carmakers and those developing Alberta’s oil sands claim new technologies will make their industries greener.
But examining the top proposed fixes shows how difficult any transformation would be. Improvements must be substantial, or dramatic increases in the number of cars and in oil sands output will overwhelm any gains in carbon reduction.
Most discussion about greener cars focuses on engine improvements. But advances are happening in other areas. Weight loss through materials such as aluminum and carbon fibre; aerodynamic designs; accessories powered by electronics instead of belts and pulleys; and continuously variable transmissions are available now and are relatively inexpensive.
These developments and modifications to conventional engines—such as direct injection and variable valve timing—each produce small fuel-economy gains that add up and are the main route for carmakers to reach the tougher emission standards taking effect in 2016.
A new technology may be a bigger leap. Homogeneous charge compression ignition, or hcci, might come through with up to 15 per cent less fuel consumption. It’s a cleaner, more complete burn that doesn’t use spark plugs. As with conventional engines, hcci mixes gasoline and air before injecting the mixture into the combustion chamber. The difference with hcci is that that the piston compresses the fuel as it rises up the cylinder, raising the fuel’s temperature until it’s hot enough to ignite.
As a result, hcci is much harder to control than spark ignition, and requires extremely precise valve timing and control of the air/gasoline mix and its temperature— not yet accomplished.
It also functions poorly at low speeds and under heavy load. Some suggest a dual system, with spark ignition part of the time, but that would add complexity and cost.
With the number of cars soaring worldwide, these changes, or even widespread adoption of conventional hybrids, won’t solve the greenhouse gas problem.
Plug-in hybrids could be better. Various manufacturers are unveiling models said to go 15 to 60 kilometres after an overnight recharge—enough mileage for most routine driving on battery power alone. Actual fuel consumption and emissions, though, will depend on how many trips stay within that range.
All-electric cars could be game-changers. Cost is a major impediment, as are current lithium ion batteries, since most are limited to less than 200 kilometres between charges.
