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I found this at Wikipedia:Hybrid vehicle#ICE-ICE Hybrid, tagged for cleanup. The commentary isn't suitable for Wikipedia, but perhaps it can be adapted or drawn on for use here. I'm hesitant to just copy it directly into an Appropedia page till we've resolved license issues:
- Nearly all motor vehicles use some form of Internal Combustion Engine, and this includes the current hybrid-electric cars such as the Prius. A basic efficiency problem of the ICE motor is that they must provide enough power for acceleration and this generally requires over 100 horsepower (75 kW). However, the amount of power needed for a typical 3,000 pound (1,350 kg) vehicle may be less than 5 horsepower (3.7 kW) when running 60 mph (95 km/h) on level roads (one term for this is "Road-Horsepower"). It is very inefficient to run a large spark-ignition (i.e. gasoline) engine under such a light load. So, in an ICE-ICE hybrid a second small motor might be used at cruising speeds. This might be wired into the common electric cruise control which many cars already have. The small motor's horsepower could be chosen with a goal of ability to allow the vehicle to climb slopes up to five degrees since few roads are truly level for even short distances. For simplicity, the small motor could have a single fixed gear ratioed to run most efficiently at a defined speed range such as 60–75 mph (95–120 km/h).
- This system would be more efficient than manufactured systems with cylinder shut-downs since those systems still have large amounts of friction—the shut-down cylinders are still running. The late Frank-Winchell of General Motors may have done work with the ICE-ICE hybrid, perhaps it is unpublished. Advantages of ICE-ICE hybrids over Petroleum-Electric hybrids would be greater range and less weight. One of the worst design flaws of the ICE-Electric vehicles is overall vehicle weight in part due to heavy batteries. But, the real waste is that 90% of the time, there is only one person in a 4–8 passenger 3,000–5,000 pound vehicle. Making a large hybrid for single person commuting is a misleading waste no matter how clever the technology. In 2002 Volkswagen showed its "One Litre Car" running concept which got over 200 mpg, weighed only about 600 pounds, was crashworthy and carried 2 people. However, the acceleration was very slow—but with a second larger motor for acceleration it could actually be quite sporty and still use very little fuel—as an ICE-ICE hybrid. A similar petroleum-electric ultralight tandem seater, the 2005 Daihatsu UFE-III could be made into an ICE-ICE hybrid for far greater range without the anchor of batteries. Also, because both of the these vehicles are only one-person wide they have a small frontal area coupled with a low drag shape. So, both are Naero vehicles (Narrow, Aerodynamic). Keep in mind that the bigger something is, the more energy it will take to move it, and there is no magic method to avoid it. Any time anyone claims superb energy efficiency, watch out for wild claims of super-high mileage, usually those are based on driving on very flat ground, with no hills and no accelerating from a start.