What is the displacement for the petrol engines model?
CREATE TABLE "engines" (
  "model" text,
  "engine" text,
  "displacement" text,
  "valvetrain" text,
  "fuel_system" text,
  "max_power_at_rpm" text,
  "max_torque_at_rpm" text,
  "years" text
);
SELECT "displacement" FROM "engines" WHERE "model"='petrol engines';