GM Displays Compression Ignition Engine
General Motors will display an advanced technology compression ignition engine at its Milford Proving Grounds in Michigan today. The engine is a peek at new internal combustion engine developments at GM. The engines have been installed in a Saturn Aura sedan and an Opel Vectra.
The concept is similar to that of a diesel, in that the fuel/air mixture is ignited by the heat caused by its compression, rather than by a spark plug. Unlike a diesel, however, the GM engines are designed to use gasoline. GM estimates that production compression ignition engines would get 15% better gas mileage than a similar conventional engine, but without the costly emissions controls needed for diesel engines to meet federal pollution standards.
The technology is not new to General Motors. In 2000, it exhibited the Precept concept car. This was a parallel hybrid which used a compression ignition direct injection engine to drive the rear wheels and a three phase electric motor to drive the front wheels. In conjunction with a very aerodynamic shape, the Precept produced 80 mpg. It was an outgrowth of the federal government sponsored “Partnership for a New Generation of Vehicles.” The goal of that program, which was launched in 1994, had been to production ready prototypes by 2004 which produced triple the gas mileage of the typical 1994 sedan.
Obviously, that didn’t happen. But, GM still seems to be pursuing the compression ignition idea. Though it is currently being displayed as a substitute for a conventional V-6 in a production car, the Precept suggests that GM may have broader purposes in developing the compression ignition concept.
The reason for the efficiency of the compression ignition engine is in the way it burns the fuel. The technical name of the engine’s design is “homogeneous charge compression ignition.” Basically, the idea is that the compression causes essentially simultaneous burning of all of the fuel in the cylinder, which creates more power for a given amount of fuel and eliminates pollutants which are by-products of incomplete combustion.
The engine is not market-ready, but GM is clearly committed to its development. According to GM’s executive director for GM Powertrain Advanced Engineering, the company has made “tremendous strides” in the technology and has shouldered “substantial” development costs, to date. But, “[a]dditional development costs, including research and testing programs, are required to make the technology ready,” he said.
The decision to display the compression ignition technology may be motivated, in part, by politics. The 35 mpg federal fuel economy standards proposed in the Senate version of the still pending federal energy bill were deleted by the House of Representatives. But there remains a risk that these provisions could be reinserted into the measure by the Congressional “conference committee” which is to reconcile the differences between the two versions of the bill.
GM, in particular, has of late seemed to be showing off its research on more fuel efficient vehicles. Though this may, to some extent, undercut the automakers’ claim that meeting the proposed standards would be hideously expensive, the display of technology which the automakers have already undertaken seems calculated to convince Congress that the automakers are already doing everything which can reasonably be expected of them to enhance fuel efficiency and pursue alternative fuels technology.