Pulse and Glide

Pulse and Glide(PnG) is also known as Burn and coast. This method consists of rapid acceleration to a given speed (the "burn" or "pulse"), followed by a period of coasting down to a lower speed, at which point the burn-coast sequence is repeated.[30] Coasting is most efficient when the engine is not running, although some gains can be realized with the engine on (to maintain power to brakes, steering and ancillaries) and the vehicle in neutral, or even with the vehicle remaining in gear.[citation needed] Most modern petrol vehicles cut off the fuel supply completely when coasting (over-running) in gear, although the moving engine adds considerable frictional drag and speed is lost more quickly than with the engine declutched from the drivetrain.

Some hybrid vehicles are well-suited to performing the burn and coast. In a series-parallel hybrid (see Hybrid vehicle drivetrain), the internal combustion engine and charging system can be shut off for the glide by simply manipulating the accelerator. However based on simulation, more gains in economy are obtained in non-hybrid vehicles.[30]
Causes of pulse-and-glide energy saving

Much of the time, automobile engines operate at only a fraction of their maximal efficiency, resulting in lower fuel economy (or what is the same thing, higher specific fuel consumption (SFC)).[31] Charts that show the SFC for every feasible combination of torque (or Brake Mean Effective Pressure) and RPM are called Brake specific fuel consumption maps. Using such a map, one can find the efficiency of the engine at various rpms, torques, etc.

During the pulse (acceleration) phase of pulse and glide, the efficiency is near maximal due to the high torque and much of this energy is stored as kinetic energy of the moving vehicle. This efficiently-obtained kinetic energy is then used in the glide phase to overcome rolling resistance and aerodynamic drag. In other words, going between periods of very efficient acceleration and gliding gives an overall efficiency that is usually significantly higher than just cruising at a constant speed. Computer calculations have predicted that in rare cases (at low speeds where the torque required for cruising at steady speed is low) it's possible to double (or even triple) fuel economy.[30]

These two- or three-fold improvements in fuel economy are possible only at city driving speeds of say 25 or 35 miles/hour. This is because cruising (steady speed) at such low speeds is very inefficient since the torque needed is so low that the efficiency read on a BSFC map is very poor. Pulse and glide significantly improves this. Unfortunately, city driving often involves many stops at signals and stop signs which were absent in the computer simulation which showed such multiple fold improvements. In other words, in the real world one is unlikely to see fuel efficiency double or triple. Such a failure is due to signals, stop signs, and considerations for other traffic; all of these factors interfering with the pulse and glide technique. But improvements in fuel economy of 20% or so are still feasible.[30][32]