What's all this petrol engine ecological-breakthrough buzzchat about – anyhow?

A major technology development that could be the eco-saviour for air-polluting internal combustion engines and our planet's atmosphere is set to become a reality.

Long considered, and quite rightly so, to be a major global contributor to atmospheric pollution, the internal combustion engine could be about to transform into a vehicle power unit that is actually more environmentally friendly than battery-powered electric vehicles (EVs).

Now, I can already hear the tree-hugging, brown-bread-and-sandals brigade spluttering into their ethically produced, spelt-enriched, additive-free bowls of granola at that piece of news.

But just as those eco-warriors adore their naturally produced and ethically-endorsed Farm-to-Bowl fodder they may well have to take notice of an automotive concept dubbed Well-to-Wheel technology.

In a nutshell it looks at the complete environmental picture when it comes to just how polluting vehicles are by analysing what happens with the oil produced at the well right through until it turns the wheels of your car. And a fundamentally important part of that is how engines burn fuel and what level of pollutants are emitted into the air we breath.

Japanese carmaker Mazda has developed a system called Spark Controlled Compression Ignition (SPCCI) which is claimed will drastically cut engine pollution while simultaneously making it more efficient in terms of fuel used and power produced.

But before getting into a more detailed explanation of that lets have a quick reality check on those supposedly cleaner-than-clean EVs. Here's a few bullet points on the subject.

1. A report by the Stuttgart-based Fraunhofer Institute for Building Physics says it takes twice the amount of energy to build an electric car as a conventional one.
2. report by the Swedish Environmental Research Institute found that battery production produces 150-200Kg of carbon dioxide equivalent per kilowatt hour (kWh) of battery produced. They say that each kilowatt hour of battery capacity involves 125 kilograms (276lbs) of CO2 emissions. For a 22 kilowatt-hour battery for a BMW i3 this equals almost 3 tons of CO2.
3. Today the UK produces most of its electricity by burning natural gas and coal which accounts for 29% of this country's greenhouse emissions. In the USA one-third of electricity is sourced from coal-fired power stations.
4. Coupled to point 3 is the fact that EV owners like to charge their cars at night. It's cheaper. But the Utility companies like to run their coal-fired power plants at night when solar power goes to sleep. A recent American study found that an electric EV charged at night created more greenhouse gas than if owners charged their EVs at random times throughout the day.
5. And one final point about electricity supply; currently there are 1.9 million battery electric vehicles in use globally compared to 1200 million conventional vehicles. This raises two points; imagine the chaos on electricity supply and greenhouse emissions if EV population ever matched that of conventional vehicles. And secondly, anything that makes conventional engines significantly less polluting must have a tremendously positively environmentally impact given the number of fossil fuel burning vehicles operating world-wide.

So before moving on to what this diesel engine breakthrough is about lets be clear on one thing. Anybody, or any organisation or any government that thinks that Electric Vehicles have a rating of zero emissions is clearly right up there in cloud-cuckoo land, particularly as two thirds of global electricity production uses fossil fuels.

The fact is that CO2 emissions of an EV can be similar to a conventional vehicle depending on the energy mix its electricity supply is created from.

So what is this Well-to-Wheel engine breakthrough? 

Mazda is looking to significantly reduce CO2 emissions from its engines. In fact the company has already publicly pledged to cut its corporate average Well-to-Wheel CO2 emissions to 50% of 2010 levels by 2030 and by 90% by 2050 Fundamentally the plan is to make engines use an extremely lean mixture of air and fuel. The mixture has such a minute amount of fuel in the air that a normal engine with spark plugs would not be able fire it.

Broadly speaking this is a concept known as known as HCCI (homogeneous charge compression ignition). It's a great idea because an engine runs cooler and creates significantly less pollutants.

But there is a fundamental problem with the idea and this is what the technologists at Mazda have solved.

The ignition of fuel at precisely the right moment is critical for the smooth efficient running of an engine and this ignition has to take place a few degrees after the engine's pistons reach TDC (top-dead-centre) which is just as they are starting their downward travel.

HCCI could not reliably provide this and would not work well in real world driving situations. So what have the technologist at Mazda done?

Mazda has developed its own compression combustion system called Spark Controlled Compression Ignition (SPCCI) that will be deployed in its new 2.0 SkyActiv-X engine.

 Spark Controlled Compression Ignition (SPCCI)

With SPCCI, the engine injects a very lean air-fuel mixture, and compresses it to 16:1. In order to ignite the mixture at precisely the right time in the engine's operating cycle a small amount of vapourised fuel is injected into the cylinder immediately around the spark plug.

This is important because when this is ignited it creates a reactionary wave in the engine's combustion chamber which in turn raises the compression and temperature to a level where the full amount of fuel in the combustion chamber is fired.

Mazda maintains that at low vehicle speeds which are typical in many urban environments these days, fuel economy can be improved by 30% and CO2 emissions cut by a similar amount.

This combustion cycle has to be precisely and reliably controlled and this is where some complex electronics comes in. The SkyActiv X engines feature not only electronic valve-timing actuators but also sensors that can measure combustion pressures in each cylinder every time it fires. This precise monitoring of engine operation conditions means the engine's control unit can make rapid adjustments on the cylinder firing sequences to make sure the engine is running at its most efficient and therefore ecological best.

So all that sounds just fine but you can rely on Mother Nature to try and throw a spanner in the works and she does exactly this by providing greatly varying weather conditions around our planet.

We know we want the fuel mixture to combust in an engine at precisely the right point but different ambient temperatures can impact on this. Let's face it there is a big difference between starting an engine on a cold winter morning in Stockholm compared to starting an already warmed-up engine that has been sitting in Madrid's summer sunshine.

The thing is these ambient temperature variations can seriously effect the time it takes for the fuel mixture to reach the correct amount of compression ignition.

The SkyActiv-X takes care of this by changing the spark timing sequence accordingly thanks to its in-cylinder sensors. As many of us know timing is everything when it comes to engines running smoothly and one of the engineering conundrums Mazda engineers had to overcome was an engine timing anomaly called pre-ignition or as its more commonly known engine knocking.

This was a very real problem because pre-ignition occurs more often with high compression engines and its serious, particularly if it causes the fuel mixture to fire before the piston has reached the top of its stroke and tries to force the piston down before the engine's crankshaft is in a position to mechanically allow that to happen.

Their solution to this puzzle was to create a way of heating the fuel/air mixture.

What happens is firstly a small initial injection is made and then the bulk of the fuel is introduced into the cylinder as late as possible during the compression stroke. This is done using multiple injectors to increase atomisation and mixing of fuel and air.

All of this makes the Mazda SkyActiv-X system a very important breakthrough relative to internal combustion engine design, which certainly means we will be using them for sometime to come. And as mentioned earlier in the article with 1200 million conventionally powered vehicles moving around our planet anything that makes them less polluting has to be applauded. Something that even those EV driving eco-warriors might agree with.

Read more on electric vehicles: Electric vehicle (EV) testing technology ramps up