MCE-5 VCRi: Pushing back the fuel consumption reduction limits

It’s clean

The MCE‑5 VCRi: To solve the CO2 vs. pollutant emissions dilemma

CO2 is not a pollutant – it’s a non-toxic greenhouse gas that is emitted in proportion to the amount of fuel consumed (the combustion of one kilogram of fuel produces roughly 3.18 kg of CO2). On the other hand, CO, HCs, NOx and particulates are toxic pollutants. The production of these pollutants by the engine is not proportional to the amount of fuel consumed but depends on the quality of combustion (homogeneity of the air-fuel mixture, flame propagation, maximum combustion temperature).

Marketing vehicles emitting pollutant levels
above the limits set by regulations is forbidden

The cost of the after-treatment systems required
by GDI stratified charge engines makes them
too expensive for small vehicles

Particulate filters and selective catalytic reduction:
Future Diesel engine after-treatment systems will
be too costly for bottom-of-the-range vehicles

As a result, the regulations applied to CO2 emissions are different from those governing CO, HC, NOx and particulates. Indeed, different financial penalties are in place to dissuade carmakers from producing cars with high CO2 emissions, while the sale of cars that emit pollutants above a certain authorized level is forbidden.

There is a contradiction in this for cars: pollutant emissions are generally inversely proportional to CO2 emissions. Gasoline cars that emit high levels of CO2 per kilometer emit fewer pollutants thanks to their 3-way catalytic converters, while Diesel cars that emit low levels of CO2 emit high levels of nitrogen oxide and particulates. This observation can also be made for the engines themselves regardless of the type: reducing the CO2 emissions of a Diesel engine increases pollutant emissions. Similarly, diverse strategies to reduce CO2 emissions applied to gasoline engines, such as lean mixtures (e.g. stratified charge), are accompanied by pollutant aftertreatment problems that, in the end, destroy their interest. Downsizing applied to gasoline engines can strongly reduce CO2 emissions, but raises the problem of high pollutant emissions at high loads, which are luckily not yet regulated.

On a technical level, it is possible to apply an aftertreatment to almost all the pollutants that engines produce before they are discharged into the atmosphere. This operation consists in transforming the pollutants produced by the engine into non-polluting elements via catalysts and/or filters. At the outlet point of these systems, we find CO2, steam and nitrogen that are identical to what is found in the atmosphere. The aftertreatment of pollutants can in some cases increase the car’s fuel consumption and CO2 emissions. An aftertreatment system can be more or less costly depending on whether it is an oxidation catalyst, a 3-way catalytic converter, a particulate filter or an SCR system (selective catalytic reduction). The quality and the size of these devices can also impact their price. Moreover, certain devices add new maintenance costs that are borne by the end customer (additives and particulate filter maintenance, urea solution for SCR systems).

The ability to comply with pollutant emission standards in the best economic, energy and strategic conditions will be vital. Depending on the case, it may bring into question certain types of engines. For example, Diesel engines are in a rather delicate position: the aftertreatment of the different pollutants that they produce is already very costly (Oxycat + particulate filter). In 2015, When the Euro VI standard comes into effect, the aftertreatment of Diesel engines will be so expensive that they may become inaccessible to low- and even medium-range cars. Diesel aftertreatment systems may reach a total cost that equals the cost of the engine itself. This could seriously decrease the market share of Diesel vehicles that could drop to 10 to 15% of European registrations in 2020, versus 53.6% in 2007. Reducing to such an extent Diesel engine market share could lead to an increase in the average CO2 emissions of certain carmakers, unless they develop gasoline engines with energy efficiencies comparable to those of Diesel engines.

Controlling pollutant emissions has both energy and economic stakes. Different methods must be used to reach the new emission levels set out in the standards. In general, one tries to avoid the engine producing pollutants with costly aftertreatment, sometimes accepting slightly higher fuel consumption levels. If an inexpensive aftertreatment is available, one will prefer to optimize the engine’s energy efficiency even if it produces more pollutants since they can be eliminated before they are released into the atmosphere. Regardless of the solution adopted, a compromise must be found between fuel consumption and CO2 emissions on one hand, and the cost price of the aftertreatment system, on the other hand.

In the end, pollutant aftertreatment impacts the profitability of the automotive product. It provides almost no advantages to the end customer, other than air that is more breathable and less harmful to their health. This collective advantage is hard to appreciate and the end customer will not be prepared to pay more for a car for just that reason, as essential as it may be. Therefore, aftertreatment is often a function that is hard to make pay.

In this context, the MCE‑5 VCRi engine provides a wide range of extremely relevant possibilities. It operates with a constant proportion air/fuel mixture, making it compatible with a simple 3-way catalytic converter, which is an effective, inexpensive aftertreatment solution. Hence, MCE‑5 VCRi does not require a particulate filter or SCR, which are by definition costly systems. Up to this point, MCE‑5 VCRi takes up the advantages already offered by most gasoline engines. Yet, MCE‑5 VCRi goes even farther. Its variable compression ratio enables it to optimize its energy efficiency and the quantity of pollutants that it produces, depending on whether its 3-way catalytic converter is ready to function or not (a temperature of roughly 240°C is necessary for the catalytic converter to be operational). During cold starts, the MCE‑5 VCRi produces very low levels of pollutants while its catalytic converter is cold but produces a lot of heat in the exhaust gases to accelerate its warm up (cat heating strategies). This strategy furthermore reduces the quantity of fuel – and therefore energy – required for catalytic converter light-off. When hot, it produces pollutants, which is inevitable to reduce average fuel consumption as much as possible, but these pollutants are transformed into non-polluting gases before being released into the atmosphere. MCE‑5’s VCRi function thereby finds the best compromise between pollutant emissions, CO2 emissions and the cost price of the 3-way catalytic converter.

These different strategies made possible by the MCE‑5 VCRi technology are vital to maximize the profitability and energy efficiency of cars in the long term, despite increasingly stringent emission standards.

The MCE‑5 VCRi is fully compatible with the 3-way catalyst, which is a popular,
affordable and efficient after-treatment system