Spark Ignition Engines: Emissions Guide

Emissions have become a focus of the automotive industry in recent years, in light of environmental concerns. Internal combustion engines are responsible for a large portion of the pollutants in our atmosphere; and so engine makers should bare responsibility for reducing this damage. Cars contribute over 15% of the global fossil fuel carbon dioxide emissions.

The main exhaust products are: Carbon dioxide, carbon monoxide, unburned hydrocarbons, nitrates, hydrogen gas, small quantities of water vapour and oxygen.

The differing levels of these products are dependent on a number of factors, many of them are sensitive the air fuel ratio within the engine. Also, the sources of these pollutants are known, and can be quantified as to their significance, but not eliminated.

For spark ignition (petrol) engines, unburned hydrocarbons come from a variety of phenomena. 5.2% come from crevices in the cylinder itself. The fuel can sit around the piston ring at the cylinder wall and not be exposed to the flame, leading to unburned gases being expelled to the environment. Other sources of this include: exhaust valve leakage, in-cylinder oxidization and quenching. Quenching is the effect of rapid cooling of the fuel at the cylinder wall preventing it from burning; this is also a source of aldehydes.

In SI Engines CO (Carbon Monoxide) is controlled mainly by the air fuel ratio (AFR). In lean mixtures (too much air for the quantity of fuel) dissociation occurs, whereby carbon dioxide decays into carbon monoxide and oxygen. They can also occur as unburned hydrocarbons partially oxidize during the exhaust stroke.

Nitrogen oxide (NOx) emissions are more complex, and are dependent on chemical reactions in series; such as the Zeldovich mechanism. Nitrogen and nitrogen oxides do increase as the temperature of the flame increases inside the cylinder. Flame speed also has an effect on the formation of NOx gases, and NOx will also increase with lower engine speeds.

So, in SI engines, CO and unburned hydrocarbons can be reduced by running with a lean mixture, but this will also lower the engine output. 

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Latest Technical F1 developments: Red Bull Exhaust

Pictures taken at Silverstone this weekend have uncovered that Red Bull have adopted or are at least testing an exhaust chamber. Also known as a Helmholz exhaust, the regular exhaust pipe features a blind addition which can accumulate exhaust gases when pressure is high in the exhaust pipe. It can then release those gases again when the driver gets off the throttle, hence evening out the pressure differences that occur in the exhaust pipe.

Apart from the evening out in an attempt to gain a more constant exhaust flow - and hence a more constant rear downforce at the diffuser - a Helmholz resonance chamber can also help the "Kadenacy Effect" in a specific RPM range of the engine.

The Kadenacy effect is an effect that forms from pressure-waves in gases. In essence, careful design of the dimensions and position of the exhaust changer can assist scavenging of exhaust gases out of the cylinders and therefore increase the pressure drop across the intake and exhaust valve area within a specific RPM range. As such it could be used to increase engine performance in the engines' most used RPM range.

To make room for the exhaust chamber that Ferrari debuted in F1 through 2011, RBR redesigned the entire exhaust of the RB8. While it previously ran close to the car's engine heat cover and then curved downward with a 180° turn, the final turn is now curved upwards, similar to Williams' exhaust layout.

Also note, as marked with yellow, the upward direction of the final 10cm of the exhaust pipe. The regulations specify that this must be a straight, circular section pointing up between 10° and 30°.

Great article came from F1Technical.net, No copyright infringment intended.

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BMW & Toyota Join Forces On Green Engines

Japanese carmaker Toyota and Germany's BMW are to work together on environmental-friendly motoring technology. They will do joint research on next-generation batteries for green cars. BMW will also supply clean 1.6 and 2 litre diesel engines to Toyota, beginning in 2014 for models for the European market.
Bosses from the two companies said they are also discussing other medium and long-term collaborative projects.

Toyota said as a result of the agreement it plans to expand its European range and sell more fuel-efficient, diesel cars. "It is a great joy and a thrill to enter into this relationship with BMW," said the company's president Akio Toyoda. BMW chairman Norbert Reithofer said that "supplying Toyota with our fuel-efficient and dynamic diesel engines represents another important step in the planned expansion of our sales activities".

"The agreement marks a milestone for ongoing cooperation between two companies that set the benchmark in complimentary field," said BMW's sales and marketing director Ian Robertson.
The BBC's Jorn Madslien, who is at the Tokyo motor show, said neither BMW nor Toyota had a lot of experience with such co-operation deals.
A similar partnership between Germany's Volkswagen and Japan's Suzuki is currently on the rocks, with Suzuki trying to force an end to the co-operation.

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Australian GP Report - Button Revels in Victory

Jenson Button hailed his victory in the Australian Grand Prix as a "dream start" to the new Formula 1 season.

Team-mate Lewis Hamilton finished third, after starting on pole , to underline McLaren's competitiveness.
"It was very important for us to get this one in the bank early on," said Button, whose lead went unchallenged after he jumped Hamilton off the line.

In contrast to the last three years, McLaren emerged strongly from pre-season testing and made it count at the opening race in Melbourne. The Woking-based team locked out the front row in qualifying and Button coasted to victory after passing Hamilton off the line.

"For the last couple of years our first races have been tricky," said Button. "I'd say we've been pretty dominant today.
"It's an amazing way to start the season.
"As a team, the win shows how important the winter is. The guys have done an amazing job. This win will definitely help them push hard in the extra hours they are doing."

Button believes the race also highlighted the increased competition throughout the field in 2012.
"We all think this is a very special year in Formula 1, having six world champions and so many competitive teams," the 2009 champion added.
"It's great to see F1 is in a great place at the moment. I'm very excited heading to [the next race in] Malaysia."
After passing Hamilton off the start, Button quickly built a lead and was unchallenged until the safety car came out on lap 37 and closed up the pack of cars.
Sebastian Vettel pitted under the safety car and came out ahead of Hamilton, who had been running in second, but Red Bull's world champion conceded he had no chance of catching Button after the restart.

"I thought I would be in a good position to have a go at Jenson but two corners and he was gone," said Vettel.
"It wasn't very easy to get away from Lewis but Jenson was out of sight. He deserved to win."
Hamilton was left to rue not only Vettel's clever strategy under the safety car but a poor start to the grand prix.
"It was a shocking start," said Hamilton, who had been determined to put a mixed 2011 season behind him in the new campaign.
"I'm not sure what happened. I let out the clutch and got a lot of wheel spin. That followed all way through the launch phase. We lost a lot of ground from there and the safety car didn't help us.

Martin Whitmarsh McLaren team boss

"It's still a great job by Jenson. Clearly we're very quick so we go forward to the next race in good shape."

When asked whether McLaren are now the dominant team, Hamilton responded: "It's too early to tell.
"In qualifying, we're quick and competitive but Red Bull were massively quick in race so they're still a force to be reckoned with."
McLaren team boss Martin Whitmarsh summed up the race weekend as "nearly perfect".
"Lewis was unlucky with the safety car," he commented. "Jenson drove majestically, he didn't put a foot wrong. It was a bit tight on fuel, we struggled a bit. But it's a great way to start the season.
"We've proved we've got a quick car [and] there'll be a few bits for the next race."

From the BBC Website

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