Petrol engine

There is still a market for the petrol engine

The drive is on to reduce CO2 emissions from cars, but despite the main focus being on electric vehicles there is life in the internal combustion engine yet.

It's hard to put a precise number on the volume of cars on the world's highways, but the best estimates claim it exceeded the one billion mark in the summer of 2010.

The total at the end of 2009 was thought to be about 980 million, and with strong growth in emerging regions - especially China, now by far the world's biggest car market - the number powered past the billion sometime during the following year.

Most analysts feel the Chinese car market is on track to cross 20 million units per year within a few years, possibly reaching as high as 40 million per year by the end of the decade. That would be three times the size of the US market, in which virtually all sales are replacements for existing vehicles.

China still has far fewer vehicles per person than western countries. With 1.3 billion of the world's almost seven billion residents, it now has 78 million vehicles, but an ownership rate of just one car per 17.2 people. That leaves a lot of room for growth; if China were to equal the US ownership rate, it would hold one billion cars all by itself.

Other growth markets include India and Brazil. In India, the ownership rate is just one car per 56.3 residents - one-third that of China.

The US, by contrast, is a mature market with the highest rate of cars per person: one car for every 1.3 people, or three cars for every four US residents. Its vehicle population of 240 million has remained steady. So how to mitigate the enormous environmental impact of such a large 'car parc', as it's known among global planners, is, to say the least, a challenge.

The seemingly blind charge of legislation and regulations aimed at reducing the carbon emissions of this billion-plus car pool are varied around the globe and often confused further by local incentives.

Meeting European targets

In Europe the CO2 emissions from cars are subject to a voluntary agreement between the EU and the car makers. The ultimate EU target is to reach an average CO2 emission (as measured according to Commission Directive 93/116/EC) of 120g/km for all new passenger cars by 2012.

The ACEA agreement, which was signed in 1998, sought to achieve an average of 140g/km of CO2 by 2008 for new passenger vehicles sold in Europe - 25 per cent reduction from the 1995 level of 186g/km, and is equivalent to a fuel economy of 5.8l/100km or 5.25l/100km for petrol and diesel engines respectively. However, the average for the whole car market for 2008 was 153.7g/km, so the target has not been achieved.

The ultimate EU target to which these agreements are to contribute is to reach an average CO2 emission (as measured according to Commission Directive 93/116/EC) of 130g/km for all new passenger cars by 2015.

The rules are different in the US - and if possible even more fragmented and confusing. They are an amalgam of national and state regulations, managed on a national level by the Environmental Protection Agency (EPA).

In Europe Volvo has been warning for some time that EU targets for cutting CO2 emissions are being jeopardised by the absence of harmonised incentives to consumers. They claim that another key issue is the urge for continuous support to automotive research and development, including electromobility.

"Volvo Car Corporation urges the EU to coordinate incentives while supporting research and development," says Stefan Jacoby, president and CEO of Volvo Car Corporation. "The European automotive industry risks losing the present technological leadership if this doesn't happen. In the long term, this jeopardises our industry's competitiveness and European jobs."

The company also raises concerns about the viability of the European Commission's White Paper on Transport, which states that greenhouse gas emissions in the transport sector will have to be cut by at least 60 per cent by 2050 to achieve the EU's climate-change goals. The paper also calls for the use of conventionally fuelled cars in cities to be halved by 2030 and then phased out by 2050.

"European car manufacturers are facing a very difficult challenge when CO2 legislations requiring electrified cars are implemented without initiatives that make these cars affordable for a growing number of consumers," Jacoby adds, raising a concern that many automakers echo about expecting too much from the incremental adoption of electric vehicles.

In 2011 fewer than 50,000 battery electric vehicles were sold in the world, equivalent to a market share of about 0.1 per cent. The figure suggests that the car market will continue to be dominated by traditional combustion-engine models for the foreseeable future.

"It is far too early to dismiss the conventional diesel and petrol power trains. We continuously improve their efficiency. In the last two years, Volvo has brought CO2 emissions from our diesel and petrol model ranges down by 13 per cent."

While there has been no official target set for the implementation of electrification within the EU, industry studies indicate that several member states are over estimating the speed at which electrified vehicles are being introduced.

The European Commission's own study, 'A European Strategy on Clean and Energy Efficient Vehicles', forecasts only 3-4 per cent market share for battery electric vehicles and plug-in hybrids by 2020, with a rise towards 30 per cent expected by 2030.

"Both predictions are unrealistic," Jacoby says. "Considering the lack of coordinated governmental incentives and the high battery-system costs, the market share for electrified vehicles will struggle to pass the 1 per cent mark by 2020."

One main reason preventing a rapid increase of electric vehicles on the roads is that the cost for the electrification technology is not being reduced fast enough. "The automotive industry's cost reduction efforts can't fully compensate for the additional battery system cost," Jacoby says. "Pan-European subsidies and incentives are needed to support a successful market introduction. Unfortunately such necessary initiatives are jeopardised by the current debt crisis."

Not all electric for Nissan

The all-electric Leaf from Nissan is leading the drive for zero emissions but the company has certainly not abandoned the internal combustion engine. The continued realisation that significant reductions in CO2 emissions from conventional engines will be necessary in the short and mid term has led them to develop one of its most technically advanced petrol engines.

The new 1.2l three-cylinder engine delivers frugal economy and an exceptionally low emissions figure of just 95g/km. Technical innovation has been packed into the engine. It uses the Miller cycle and direct petrol injection with a compression ratio of 13 to 1 for greater efficiency and a supercharger for instant throttle response and added power.

The engine will make its debut in the latest Nissan Micra. "When it comes to performance figures, the first one that city car buyers look at these days is emissions performance," Pierre Loing, vice president product strategy and planning, Nissan International, says. "The Direct Injection Gasoline-Supercharger certainly tops the emissions tables, but the clever technology under the bonnet also means its 'conventional' performance is equally impressive.

"With the instant responses and refinement only a petrol engine can provide, coupled to a taut yet comfortable new platform, and plenty of advance technology like PSM the new Micra is equally at home on the open road as it is in the city."

As well as delivering ultra-low CO2 emissions, the lightweight, low-friction 1,198cc DIG-S three-cylinder unit produces the power expected from a conventional 1.5l four-cylinder engine. Further efficiency gains are made by the adoption of advanced engine management systems with start/stop and energy regeneration.

Two technologies designed to reduce losses and enhance combustion efficiency - the Miller combustion cycle and a supercharger - are key to the reduced emissions. By minimising heat, friction and pumping losses as much as possible and combining it with an unusually high compression ratio of 13 to 1, Nissan's engineers have created an engine that sets the standard for the rest of the industry.

Friction is reduced by a nano-level polish on its sliding surfaces of the camshaft bearing, while diamond-like carbon (DLC) coatings are used on the valve lifters and the piston rings. The hydrogen-free DLC coating cuts friction by as much as 50 per cent on the valve lifters and 18 per cent on the piston rings, compared with no coating.

The Miller combustion cycle raises the compression ratio - in this case to 13 to 1 - by modifying the conventional Otto four stroke cycle. It leaves the intake valve open longer, effectively turning the compression stroke into two separate cycles: part one when the valve opens, part two when it closes. With this two-stage intake stroke, the Miller cycle is ideally suited to direct fuel injection technology.

When the piston moves upwards at the start of the compression stroke, resistance is less because the intake valve is still open, which results in lower pumping losses. At the same time the temperature of the mixture is lowered thanks to the delay in the start of the combustion process, which happens at a point about 25 per cent into the combustion stroke.

To overcome the potential loss in power caused by the expulsion of the charge in the initial stage of the stroke, the engineers have adopted a supercharger to boost power. The intake air is compressed by the supercharger and then cooled with the result that the lower charge temperature permits the ignition timing to be advanced without fear of detonation or knock, thus improving overall efficiency still further.

Designed for diesel

For Renault's latest diesel engine an assortment of innovative technologies such as downsizing, Stop&Start, regenerative braking system and low-pressure EGR (exhaust gas recirculation) help achieve a 20 per cent gain in CO2 emissions.

The greatest saving, 5.5 per cent, came from downsizing and the incorporation of new technologies, as well as a 'square' architecture which takes its inspiration from the world of Formula 1.

Downsizing was obtained by reducing piston stroke and the size of the moving parts (crankpin and conrod). The swept volume of the cylinder has been reduced by 16 per cent which has reduced the amount of fuel consumed during each cycle.

As its name implies, Stop&Start technology involves automatically cutting the engine when the vehicle is at a standstill because the engine clearly doesn't emit any pollutants or CO2 when it isn't running. This system comes into its own in built-up areas and congested traffic. When running exclusively in built-up areas, fuel savings can exceed a litre per 100km. The system comprises a controller which instructs the ECU to cut the engine when three conditions are met: the transmission is in neutral, the clutch pedal is released and the car's speed is close to zero.

When the driver presses on the clutch to select first gear, the ECU is instructed to re-start the engine, which fires up instantly, allowing the vehicle to move away. To cope with the engine's repeated starting, the specification of the starter motor has been uprated (starter, starter ring gear), as has the fuel injection system (pump and high-pressure injectors). The engine automatically restarts if it stalls.

The regenerative braking system allows an extra CO2 saving of 3 per cent, allowing the kinetic energy produced under deceleration/braking - which is traditionally dissipated in the form of heat via the brake discs - to be recovered. This energy is recovered by the alternator and stored in the battery. Functions which consume electricity (heater, lights, radio, etc) are directly fed by the battery to ease the work of the alternator.

These two are far from an exception. Every motor manufacturer has its brand for fuel efficient, low-emission engines such as BMW's EfficientDynamics, Honda's Integrated Motor Assist, Mercedes-Benz's BlueEFFICIENCY and Volkswagen's BlueMotion, and that drive will continue as the venerable Internal Combustion Engine continues to defy the critics who have proclaimed that its days are over. 

Recent articles

Info Message

Our sites use cookies to support some functionality, and to collect anonymous user data.

Learn more about IET cookies and how to control them

Close