Oxides of nitrogen in Petrol engine exhaust can be reduced by the following methods:
1. Use of 5% lean mixture
2. Advancing the spark timing
3. Recirculating a fraction of exhaust gas
4. Using an oxidation catalyst in the exhaust manifold
Which of the above statements is/are correct?1
1 and 2
2
2 only
3
3 and 4
4
3 only