Exhaust gas control device of gas engine
An object is to provide an exhaust-gas control device for a gas engine whereby NOx is reduced and fuel consumption is improved by performing NOx restriction operation when an environmental or geographical condition in which the amount of NOx emission needs to be temporarily restricted is satisfied, and otherwise performing stable operation focusing on the fuel consumption. The exhaust-gas control device for a gas engine includes: a basic operation mode unit ( 80 ) using the first target ignition timing and the first target air-fuel rate at which the fuel consumption rate is the optimum; a low-NOx operation mode unit ( 82 ) using the second target ignition timing retarded from the first target ignition timing and the second target air-fuel rate increased from the first target air-fuel rate; a NOx reduction demand determination unit ( 86 ) for determining whether to restrict the amount of NOx emission temporarily, and an switching unit to operation mode ( 84 ) for switching the operation mode to the low NOx operation mode while the reduction demand condition is satisfied by the NOx reduction demand determination unit.
1. An exhaust-gas control method for a gas engine, which mixes fuel gas and air and supplies mixed gas to a combustion chamber, comprising:
executing a basic operation mode in which an ignition-timing of the mixed gas and an air-fuel rate in the combustion chamber are respectively controlled to be a first target ignition timing and a first target air-fuel rate which are respectively set as an ignition timing and an air-fuel rate at which a fuel consumption rate is the best on the basis of an engine speed and an engine load;
determining whether there is a NOx reduction demand to restrict an amount of NOx emission temporarily, on the basis of at least one of a geographical condition of a region where the amount of NOx emission is regulated, or an engine operation elapse condition;
switching an operation mode from the basic operation mode to a low NOx operation mode in which the ignition-timing and the air-fuel rate are respectively controlled to be a second target ignition timing retarded from the first target ignition timing and a second target air-fuel rate increased from the first target air-fuel rate as target values;
continuing the low NOx operation mode until a NOx reduction demand is cancelled; and
switching the operation mode from the low NOx operation mode to the basic operation mode when the NOx reduction demand is cancelled.
2. The exhaust-gas control method for a gas engine according to claim 1 , wherein the NOx reduction demand incorporates a high-temperature and low-humidity condition that an ambient temperature in which the gas engine is installed is a predetermined value or more and a humidity is a predetermined value or less.
3. The exhaust-gas control method for a gas engine according to claim 1 , wherein the NOx reduction demand is determined that there is a necessity when a predetermined period before a next maintenance time elapses, or a predetermined period after a start of first operation elapses, on the basis of operation-time data of the gas engine.
4. The exhaust-gas control method for a gas engine according to claim 1 , wherein the NOx reduction demand is determined that there is a necessity when a moving body equipped with the gas engine enters a region where the amount of NOx emission is regulated.
5. The exhaust-gas control method for a gas engine according to claim 1 , wherein the gas engine includes a turbocharger, and the air-fuel rate is increased by controlling the turbocharger in the low NOx operation mode.
6. The exhaust-gas control method for a gas engine according to claim 1 , wherein the gas engine has a pilot-injection combustion-chamber structure, and the air-fuel rate is increased in the low NOx operation mode by reducing pilot fuel which is injected into a precombustion chamber or a main chamber.