To reduce CO2 emissions, it is necessary to increase the fuel economy. This implies extracting the kinetic energy from the combustion energy with minimum losses.
Using a leaner air-fuel ratio is recommended, this will result in the reduction of unburnt fuel left behind. Increasing Compression ratio, increasing compression ratio increases the efficiency of the combustion process. If the mixture is more compressed, the temperatures will be higher, even before the spark and the combustion will be more complete, decreasing CO emissions.
Proper engine tuning is also an important step. The Engine relies on a lot of different systems to operate, including fuel injection, timing, transmission, and other important functions. Engine tuning allows you to fine-tune those processes to get a much cleaner burn. Downsizing of transmission, by reducing the weight of the transmission, reduces the load on the engine thereby reducing unburnt hydrocarbon emissions.
Friction losses can be reduced by replacing the sliding components with bearings where ever possible.By using biofuels (Ethanol) instead of fossil fuels, Ethanol and other biofuels are often touted for their ability to reduce greenhouse gas emissions by replacing fossil fuels. Traditional biofuels like ethanol can reduce greenhouse gas emissions by 19-48 percent compared with gasoline, while advanced or cellulosic biofuels can reduce emissions by more than 100 percent.