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Comparison: KTM LC 4 with and without emission control

theory and practice

In theory, a secondary air system is the optimal addition to the uncontrolled catalytic converter. In addition to the lower pollution caused by the pollutant components hydrocarbons (HC) and carbon monoxide (CO), the post-oxidation also heats up the exhaust gases and thus accelerates the start-up of the catalytic converter. In 1991, MOTORRAD put this knowledge into practice in a BMW R 80 GS – with resounding success. The emissions of the components HC and CO fell by 85 to 90 percent, nitrogen oxides (NOx) fell by 50 percent. These are conversion rates that are in the range of a regulated catalytic converter.
So it is all the more gratifying that with KTM, a manufacturer finally brought the inexpensive and effective system on the market for the LC 4 models with electric starter (except for the Adventure).
But all theory is gray. At least that’s what it seemed when MOTORRAD compared an LC 4 with one without an emission control system on the test bench. The motorcycle without pollutant aftertreatment emitted low HC and NOx concentrations with which it could easily have mastered the future Euro I standard, but with hydrocarbons it just barely made it through the current hurdle of the ECE-40 cycle. The amazing thing about the LC 4 with Kat and SLS: Although the HC and NOx concentrations were 50 to 75 percent lower than without exhaust gas cleaning, the carbon monoxide reached values ​​that a well-tuned motorcycle without pollutant cleaning also achieved.
Inquiries at KTM brought amazing things to light. The lack could be due to the wrong carburetor equipment. The LC 4 LSE completed the homologation with a throttle valve with a 50 cutout. Dellorto cannot deliver that at the moment. Therefore, contrary to the general operating permit, KTM is currently installing slides with at 40 cutout.
In order to get to the bottom of the misery, MOTORRAD set a new date on the emissions test bench and tried to optimize the system together with homologation specialist Joachim Sauer from KTM. Measurements of the CO content while idling already indicated that the setting was too rich. After adjusting the air control screw, there was a surprising turnaround even with the 40 mm slider. CO and HC fell drastically, and even the inherently low NOx decreased even further, all concentrations that easily undercut the limit values ​​of the Euro I standard planned for the future. The assembly of the homologated 50 mm valve brought another improvement. Compared to the baseline, HC fell by 90 percent and CO by 96 percent, while NOx alone rose by ten percent. All values ​​that can easily withstand the comparison of modern motorcycles with a regulated catalytic converter.
Tea manufacturer can only exploit the potential of the inexpensive system – including installation, in total no more than around 200 marks in production – if the basic requirements are right. The catalytic converter only works optimally in its most favorable operating range around lambda = 1. At the moment the final inspection of around 100 vehicles built per day records the idle CO for exactly two.
HHere, the gap between theory and practice can only be closed by extensive control and subsequent sealing of the mixture control screw. Then maybe the last yesterday’s representatives of Japanese motorcycle manufacturers who are still successfully combating the use of efficient exhaust gas cleaning systems at the expense of the environment can be convinced. In your opinion, there is no need for action, as all current models meet the applicable emission limit values. Measured against the current slack limit values, this seems a theory that is not very practical.

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