Features and technology / Features in general
Special engine features Emission reduction
Basically there are three ways of reducing the main emission components NOx, carbon monoxide (CO) and unburned total hydrocarbons (THC) of combustion engines:
• Measures within the engine • Exhaust gas after treatment • Combination of both
The alternative concept is the so called lean-burn concept, where excess air in the combustion chamber allows already low NOx emissions without exhaust gas after treatment.
Lean-burn concepts typically exhibit NOx emissions in the range of NOx ~ 250mg/Nm³ (~ 0.6g / bhp_hr) without catalytic exhaust gas after treatment, the rich-burn concept shows significantly higher NOx emissions (NOx ~ 4 – 6,000 mg/Nm³) in the untreated exhaust gas. But with the help of a three way catalyst, significantly lower NOx emission levels (NOx < 50mg/Nm³ / ~0.1g/bhp_hr) in combination with very low CO and HC-emissions can be achieved. In addition this concept shows in general higher exhaust gas temperatures, which is beneficial for e.g. heat recovery and a better load response e.g. at transient loads. Rich-burn engines are due to the high combustion temperature at stoichiometric conditions limiting achievable specific output, respectively mean effective pressure which results in lower efficiency levels compared to lean-burn engines.
0.8 0.9 NOx 1.0 1.1 1.2 Total HC 1.3 1.4 1.5
Air fuel ratio (λ) CO
1.6 1.7 1.8 1.9 2.0 2.1
Another method used to achieving similar low levels of NOx in natural gas operation like at rich-burn engines is the combination of a Selective Catalytic Reduction (SCR) with lean-burn combustion. With this method, it is necessary to inject a controlled amount of
NOx reduction by exhaust gas after-treatment
In the case of very low limits for NOx there are two methods available. One is the so called Lambda = 1 or Rich Burn concept. Based on a very precise control of the air fuel ratio at stoichiometric conditions rich burn engines can achieve very low exhaust gas emissions for e.g. NOx, CO or THC by help of a three way catalyst with extraordi- nary high conversion ratios (NOx app. 99 %, CO app. 95 %).
urea in front of the catalyst to ensure the reduction of NOx to N2. This method provides the advantage of operating the engine in the lean-burn mode with an optimal air-fuel ratio, and hence high levels of efficiency and high mean effective pressures. This method is generally used in all greenhouse installations with CO2 fertilization.
The most widely used method for NOx reduction is lean burn concept, which is in Jenbacher gas engines called LEANOX*. While Jenbacher offers only lean-burn engines, Waukesha is able to offer both combustion control concepts for the VGF* and VHP* platform.
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Emissions
(λ = 1 Concept)
NSCR
Lean combustion Misfiring
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