The race is on to develop petrol engines that are as efficient as diesel engines. Petrol engines produce far fewer emissions than their diesel counterparts and so are prime targets for advanced technologies- such ad turbochargers and superchargers-that boost power.

Homogenous charge compression ignition technology (HCCI) –that Gmis debuting in a Vauxhall Vectra and a Saturn Aura – enables conventional petrol engines to approach a similar level of engine efficiency to diesels.

Not only is the new system adaptable to today’s standard petrol engine architectures and compatible with all commercially available petrol, it is also compatible with bio-ethanol E85 fuel.

When combined with other advanced technologies including direct injection, electric cam phasing, variable valve lift and cylinder pressure sensing, HCCI provides up to 15 per cent fuel savings, while meeting future emissions standards.

“I remember debating this combustion capability when I was in college,” says Tom Stephens, group vice president, GM Powertrain and Quality. “It was just a dream then . Today, using maths-based predictive analysis and other tools, we are beginning to see how we can make this technology real. By combining HCCI with other advanced petrol engine and control technologies we can deliver good fuel asvings for consumers.”

The engine

In an integrated engine concept, HCCI approaches the engine efficiency of a diesel, without the need for expensive lean nitrogen oxide (NO_x) after-treatment systems. The engine is efficient because it burns fuel at lower temperatures and reduces the heat energy lost during the combustion process. Consequently, less carbon dioxide (CO₂) is released.

The HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder. Unlike a  spark ignition petrol or diesel engine, HCCI produces a low – temperature,flameless release of energy throughout the entire combustion chamber. All of the fuel in the chamber is burned simultaneously. This prouces power similar to today’s conventionall petrol engines, but uses less fuel to do it.

A traditional spark ignition is still used when the engine is started cold to generate heat within the cylinders and quickly heat up the exhaust catalyst an enable HCCI operation. During HCCI mode, the mixture’s dilution is comparatively lean, meaning there is a larger percentage of air in the micture. The lean operation of HCCI helps the engine approach the efficiency of a diesel but it requires only a conventional automotive exhaust after-treatment.

HCCI builds on the integration of other advanced engine technologies-some of which are already in production and can be adapted to existing petrol engines. The cylinder compression ration is similar to a conventional direct injection petrol engine and is compatible with all commercially available petrol and bio-ethanol E85 fuels.

A sophisticated controller uses cylinder pressuer sensors and GM-developed control algorithms to manage the HCCI combustion process. It also manages the transition between HCCI combustion and conventional spark-ignition combustion. The transition between the combustion processes is notable in the demonstration prototypes, but production versions are intended to deliver a seamless transition while driving, similar to the deactivation performance of GM’s Active Fuel Management system.

“Perhaps the biggest challenge of HCCI is controlling the combustion process,” says Professor Uwe Grebe, executive director for GM Powertrain Advanced Engineering.”With spark ignition, you can adjust the timing and intensity of the spark but with but with HCCI’s flameless combustion, you need to change the mixture composition and temperature in a complex and timely manner to achieve comparable performance.”

Concept vehicles

The HCCI-powered concept vehicles-the Aura and the Vectra, both with a modified 2.2-litre four-cylinder engine-drive like conventionally powered vehicles, but are up to 15 per cent more efficient compared to a port fuel injected engine (these fuel efficiency improvements will vary depending on the vehicle and the customer driving cycle).

The driveable concept vehicles represent one of the first tangible demonstrations of HCCI technology outside of the laboratory. “This is another initiative in GM’s advanced propulsion technology strategy to lessen our dependence on oil,” says Stevens.”HCCI, direct- injection, variable valve timing and lift, and Active Fuel Management all help improve the fuel economy and performance of our internal combustion engines. I am confident that HCCI will one day have a place within our portfolio of future fuel saving technologies.”

参考译文：

提高汽油机的效率从而使它拥有和柴油机相同效率的竞赛正在展开。汽油机产生的排放远比柴油机的少得多，所以汽油机发展的主要目标在于开发提高推进动力的先进科技，例如涡轮增压和机械增压等。

均质预混合压燃着火技术（HCCI）被通用汽车公司首次用于Vauxhall Vectra 和Saturn Aura上，使用这项技术使得传统的汽油机达到了同等型号的柴油机的效率水平。

这套新系统不光适应于当今的标准汽油机结构和所有的市面上提供的汽油，同样它也适用于生物乙醇E85燃料。

当均质预混合压燃着火技术（HCCI）和其他先进的技术，其中包括缸内直喷，电子凸轮定位，可变阀门升程和缸内压力感应共同使用时，能够节约15%的燃油，同时满足未来的排放标准。

“我记得当我在大学时曾经围绕这个燃烧能力产生争论”通用公司动力和质量部门副经理Tom Stephens谈到，“当时这只是一个梦。今天我们利用基于数学的预示分析法和其他工具，看看我们如何实现这项技术。通过HCCI和其他先进汽油机控制技术，我们能够为消费者节约大量的燃油消耗。”

发动机

在一个完整的发动机概念里，HCCI在没有使用昂贵的稀氮氧化物（NO_x）后处理系统，达到了柴油机的效率。发动机之所以高效是因为在一个较低的温度燃料燃烧，从而在燃烧过程中减少了热能的流失。因此，也排放了更少的二氧化碳（CO₂）。

HCCI发动机通过在缸内压缩燃料和空气的混合物来点燃。和汽油机，柴油机的点燃方式不同，HCCI在整个燃烧室提供了一种低温的，无火焰的能量释放。燃烧室内所有的燃料同时燃烧，这产生了今天传统汽油发动机的功率，但是只用了更少的燃料来实现。

当发动机冷启动时，要在缸内产生热量，同时快速得加热废气催化器，启动HCCI，仍旧是用传统的点燃方式。在HCCI模式中，混合燃料相对较稀，以为着有大量的的空气在混合燃料内。HCCI的稀燃帮助发动机接近柴油机的效率但是它需要的只是一个传统汽车尾气后处理装置。

HCCI建立在其它先进发动机技术的综合基础之上，有些技术基础已经投入到实际生产并适合现在的汽油机。缸内压缩比和传统的直喷汽油机类似，同时适用于各种市售的汽油和生物酒精E85燃料。

常用的控制器使用缸内压力传感器和通用公司开发的控制算法来处理HCCI的燃烧过程。同时它也进行HCCI燃烧和传统点燃燃烧之间的转换。燃烧过程之间的转换在展示模型中值得关注，但产品在驾驶时则要体现没有区别的转换，和通用的智能燃油控制系统的关闭功能类似。

“可能HCCI最大的挑战在于控制燃烧过程，”通用高级动力系统工程部门执行理事，Uwe Grebe教授说。“如果使用点燃方式，你能够调整正时和火花强度，但是采用HCCI的无焰燃烧方式，你需要改变混合燃料的组成，同时温度也是一个复杂，对于时间有高要求的变量来达到相当的性能。”

概念汽车

HCCI动力概念汽车－Aura和Vectra都采用了改良的2.2升四缸发动机，行驶性能和传统动力汽车相同，但是和进气道喷射发动机相比高效多达15%（这些燃油效率的提高量的多少主要车辆和乘客的行驶工况来决定）。

可行驶的概念汽车代表了HCCI科技在实验室外的第一次切实展示。“这是通用公司减少燃油依赖的先进动力技术策略的又一项创新”，Stevens说。“HCCI，缸办直喷，可变正时相位和气门升程，和智能燃油控制将帮助提高燃油经济性和我们内燃机的性能。我有信息HCCI将有一天在我们将来的燃油技术组合之中占有一席之地。”